Michael S. Tsirkin
2015-Dec-31 19:05 UTC
[PATCH v2 00/34] arch: barrier cleanup + barriers for virt
Changes since v1: - replaced my asm-generic patch with an equivalent patch already in tip - add wrappers with virt_ prefix for better code annotation, as suggested by David Miller - dropped XXX in patch names as this makes vger choke, Cc all relevant mailing lists on all patches (not personal email, as the list becomes too long then) I parked this in vhost tree for now, but the inclusion of patch 1 from tip creates a merge conflict (even though it's easy to resolve). Would tip maintainers prefer merging it through tip tree instead (including the virtio patches)? Or should I just merge it all through my tree, including the duplicate patch, and assume conflict will be resolved? If the second, acks will be appreciated. Thanks! This is really trying to cleanup some virt code, as suggested by Peter, who said> You could of course go fix that instead of mutilating things into > sort-of functional state.This work is needed for virtio, so it's probably easiest to merge it through my tree - is this fine by everyone? Arnd, if you agree, could you ack this please? Note to arch maintainers: please don't cherry-pick patches out of this patchset as it's been structured in this order to avoid breaking bisect. Please send acks instead! Sometimes, virtualization is weird. For example, virtio does this (conceptually): #ifdef CONFIG_SMP smp_mb(); #else mb(); #endif Similarly, Xen calls mb() when it's not doing any MMIO at all. Of course it's wrong in the sense that it's suboptimal. What we would really like is to have, on UP, exactly the same barrier as on SMP. This is because a UP guest can run on an SMP host. But Linux doesn't provide this ability: if CONFIG_SMP is not defined is optimizes most barriers out to a compiler barrier. Consider for example x86: what we want is xchg (NOT mfence - there's no real IO going on here - just switching out of the VM - more like a function call really) but if built without CONFIG_SMP smp_store_mb does not include this. Virt in general is probably the only use-case, because this really is an artifact of interfacing with an SMP host while running an UP kernel, but since we have (at least) two users, it seems to make sense to put these APIs in a central place. In fact, smp_ barriers are stubs on !SMP, so they can be defined as follows: arch/XXX/include/asm/barrier.h: #define __smp_mb() DOSOMETHING include/asm-generic/barrier.h: #ifdef CONFIG_SMP #define smp_mb() __smp_mb() #else #define smp_mb() barrier() #endif This has the benefit of cleaning out a bunch of duplicated ifdefs on a bunch of architectures - this patchset brings about a net reduction in LOC, even with new barriers and extra documentation :) Then virt can use __smp_XXX when talking to an SMP host. To make those users explicit, this patchset adds virt_xxx wrappers for them. Touching all archs is a tad tedious, but its fairly straight forward. The rest of the patchset is structured as follows: -. Patch 1 fixes a bug in asm-generic. It is already in tip, included here for completeness. -. Patches 2-12 make sure barrier.h on all remaining architectures includes asm-generic/barrier.h: after the change in Patch 1, code there matches asm-generic/barrier.h almost verbatim. Minor code tweaks were required in a couple of places. Macros duplicated from asm-generic/barrier.h are dropped in the process. After all that preparatory work, we are getting to the actual change. -. Patches 13 adds generic smp_XXX wrappers in asm-generic these select __smp_XXX or barrier() depending on CONFIG_SMP -. Patches 14-27 change all architectures to define __smp_XXX macros; the generic code in asm-generic/barrier.h then defines smp_XXX macros I compiled the affected arches before and after the changes, dumped the .text section (using objdump -O binary) and made sure that the object code is exactly identical before and after the change. I couldn't fully build sh,tile,xtensa but I did this test kernel/rcu/tree.o kernel/sched/wait.o and kernel/futex.o and tested these instead. Unfortunately, I don't have a metag cross-build toolset ready. Hoping for some acks on this architecture. Finally, the following patches put the __smp_xxx APIs to work for virt: -. Patch 28 adds virt_ wrappers for __smp_, and documents them. After all this work, this requires very few lines of code in the generic header. -. Patches 29,30,33,34 convert virtio xen drivers to use the virt_xxx APIs xen patches are untested virtio ones have been tested on x86 -. Patches 31-32 teach virtio to use virt_store_mb sh architecture was missing a 2-byte smp_store_mb, the fix is trivial although my code is not optimal: if anyone cares, pls send me a patch to apply on top. I didn't build this architecture, but intel's 0-day infrastructure builds it. tested on x86 Davidlohr Bueso (1): lcoking/barriers, arch: Use smp barriers in smp_store_release() Michael S. Tsirkin (33): asm-generic: guard smp_store_release/load_acquire ia64: rename nop->iosapic_nop ia64: reuse asm-generic/barrier.h powerpc: reuse asm-generic/barrier.h s390: reuse asm-generic/barrier.h sparc: reuse asm-generic/barrier.h arm: reuse asm-generic/barrier.h arm64: reuse asm-generic/barrier.h metag: reuse asm-generic/barrier.h mips: reuse asm-generic/barrier.h x86/um: reuse asm-generic/barrier.h x86: reuse asm-generic/barrier.h asm-generic: add __smp_xxx wrappers powerpc: define __smp_xxx arm64: define __smp_xxx arm: define __smp_xxx blackfin: define __smp_xxx ia64: define __smp_xxx metag: define __smp_xxx mips: define __smp_xxx s390: define __smp_xxx sh: define __smp_xxx, fix smp_store_mb for !SMP sparc: define __smp_xxx tile: define __smp_xxx xtensa: define __smp_xxx x86: define __smp_xxx asm-generic: implement virt_xxx memory barriers Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb" virtio_ring: update weak barriers to use __smp_XXX sh: support a 2-byte smp_store_mb virtio_ring: use virt_store_mb xenbus: use virt_xxx barriers xen/io: use virt_xxx barriers arch/arm/include/asm/barrier.h | 35 ++----------- arch/arm64/include/asm/barrier.h | 19 +++---- arch/blackfin/include/asm/barrier.h | 4 +- arch/ia64/include/asm/barrier.h | 24 +++------ arch/metag/include/asm/barrier.h | 55 ++++++------------- arch/mips/include/asm/barrier.h | 51 ++++++------------ arch/powerpc/include/asm/barrier.h | 33 ++++-------- arch/s390/include/asm/barrier.h | 25 ++++----- arch/sh/include/asm/barrier.h | 11 +++- arch/sparc/include/asm/barrier_32.h | 1 - arch/sparc/include/asm/barrier_64.h | 29 +++------- arch/sparc/include/asm/processor.h | 3 -- arch/tile/include/asm/barrier.h | 9 ++-- arch/x86/include/asm/barrier.h | 36 +++++-------- arch/x86/um/asm/barrier.h | 9 +--- arch/xtensa/include/asm/barrier.h | 4 +- include/asm-generic/barrier.h | 102 ++++++++++++++++++++++++++++++++---- include/linux/virtio_ring.h | 22 +++++--- include/xen/interface/io/ring.h | 16 +++--- arch/ia64/kernel/iosapic.c | 6 +-- drivers/virtio/virtio_ring.c | 15 +++--- drivers/xen/xenbus/xenbus_comms.c | 8 +-- Documentation/memory-barriers.txt | 28 ++++++++-- 23 files changed, 266 insertions(+), 279 deletions(-) -- MST
Michael S. Tsirkin
2015-Dec-31 19:05 UTC
[PATCH v2 01/32] lcoking/barriers, arch: Use smp barriers in smp_store_release()
From: Davidlohr Bueso <dave at stgolabs.net> With commit b92b8b35a2e ("locking/arch: Rename set_mb() to smp_store_mb()") it was made clear that the context of this call (and thus set_mb) is strictly for CPU ordering, as opposed to IO. As such all archs should use the smp variant of mb(), respecting the semantics and saving a mandatory barrier on UP. Signed-off-by: Davidlohr Bueso <dbueso at suse.de> Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org> Cc: <linux-arch at vger.kernel.org> Cc: Andrew Morton <akpm at linux-foundation.org> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org> Cc: Heiko Carstens <heiko.carstens at de.ibm.com> Cc: Linus Torvalds <torvalds at linux-foundation.org> Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz at infradead.org> Cc: Thomas Gleixner <tglx at linutronix.de> Cc: Tony Luck <tony.luck at intel.com> Cc: dave at stgolabs.net Link: http://lkml.kernel.org/r/1445975631-17047-3-git-send-email-dave at stgolabs.net Signed-off-by: Ingo Molnar <mingo at kernel.org> --- arch/ia64/include/asm/barrier.h | 2 +- arch/powerpc/include/asm/barrier.h | 2 +- arch/s390/include/asm/barrier.h | 2 +- include/asm-generic/barrier.h | 2 +- 4 files changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h index df896a1..209c4b8 100644 --- a/arch/ia64/include/asm/barrier.h +++ b/arch/ia64/include/asm/barrier.h @@ -77,7 +77,7 @@ do { \ ___p1; \ }) -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0) +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) /* * The group barrier in front of the rsm & ssm are necessary to ensure diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h index 0eca6ef..a7af5fb 100644 --- a/arch/powerpc/include/asm/barrier.h +++ b/arch/powerpc/include/asm/barrier.h @@ -34,7 +34,7 @@ #define rmb() __asm__ __volatile__ ("sync" : : : "memory") #define wmb() __asm__ __volatile__ ("sync" : : : "memory") -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0) +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) #ifdef __SUBARCH_HAS_LWSYNC # define SMPWMB LWSYNC diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h index d68e11e..7ffd0b1 100644 --- a/arch/s390/include/asm/barrier.h +++ b/arch/s390/include/asm/barrier.h @@ -36,7 +36,7 @@ #define smp_mb__before_atomic() smp_mb() #define smp_mb__after_atomic() smp_mb() -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0) +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) #define smp_store_release(p, v) \ do { \ diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index b42afad..0f45f93 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -93,7 +93,7 @@ #endif /* CONFIG_SMP */ #ifndef smp_store_mb -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); mb(); } while (0) +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) #endif #ifndef smp_mb__before_atomic -- MST
Michael S. Tsirkin
2015-Dec-31 19:05 UTC
[PATCH v2 02/32] asm-generic: guard smp_store_release/load_acquire
Allow architectures to override smp_store_release and smp_load_acquire by guarding the defines in asm-generic/barrier.h with ifndef directives. This is in preparation to reusing asm-generic/barrier.h on architectures which have their own definition of these macros. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- include/asm-generic/barrier.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index 0f45f93..987b2e0 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -104,13 +104,16 @@ #define smp_mb__after_atomic() smp_mb() #endif +#ifndef smp_store_release #define smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ smp_mb(); \ WRITE_ONCE(*p, v); \ } while (0) +#endif +#ifndef smp_load_acquire #define smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ @@ -118,6 +121,7 @@ do { \ smp_mb(); \ ___p1; \ }) +#endif #endif /* !__ASSEMBLY__ */ #endif /* __ASM_GENERIC_BARRIER_H */ -- MST
asm-generic/barrier.h defines a nop() macro. To be able to use this header on ia64, we shouldn't call local functions/variables nop(). There's one instance where this breaks on ia64: rename the function to iosapic_nop to avoid the conflict. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Tony Luck <tony.luck at intel.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/ia64/kernel/iosapic.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/ia64/kernel/iosapic.c b/arch/ia64/kernel/iosapic.c index d2fae05..90fde5b 100644 --- a/arch/ia64/kernel/iosapic.c +++ b/arch/ia64/kernel/iosapic.c @@ -256,7 +256,7 @@ set_rte (unsigned int gsi, unsigned int irq, unsigned int dest, int mask) } static void -nop (struct irq_data *data) +iosapic_nop (struct irq_data *data) { /* do nothing... */ } @@ -415,7 +415,7 @@ iosapic_unmask_level_irq (struct irq_data *data) #define iosapic_shutdown_level_irq mask_irq #define iosapic_enable_level_irq unmask_irq #define iosapic_disable_level_irq mask_irq -#define iosapic_ack_level_irq nop +#define iosapic_ack_level_irq iosapic_nop static struct irq_chip irq_type_iosapic_level = { .name = "IO-SAPIC-level", @@ -453,7 +453,7 @@ iosapic_ack_edge_irq (struct irq_data *data) } #define iosapic_enable_edge_irq unmask_irq -#define iosapic_disable_edge_irq nop +#define iosapic_disable_edge_irq iosapic_nop static struct irq_chip irq_type_iosapic_edge = { .name = "IO-SAPIC-edge", -- MST
Michael S. Tsirkin
2015-Dec-31 19:06 UTC
[PATCH v2 04/32] ia64: reuse asm-generic/barrier.h
On ia64 smp_rmb, smp_wmb, read_barrier_depends, smp_read_barrier_depends and smp_store_mb() match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Tony Luck <tony.luck at intel.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/ia64/include/asm/barrier.h | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h index 209c4b8..2f93348 100644 --- a/arch/ia64/include/asm/barrier.h +++ b/arch/ia64/include/asm/barrier.h @@ -48,12 +48,6 @@ # define smp_mb() barrier() #endif -#define smp_rmb() smp_mb() -#define smp_wmb() smp_mb() - -#define read_barrier_depends() do { } while (0) -#define smp_read_barrier_depends() do { } while (0) - #define smp_mb__before_atomic() barrier() #define smp_mb__after_atomic() barrier() @@ -77,12 +71,12 @@ do { \ ___p1; \ }) -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) - /* * The group barrier in front of the rsm & ssm are necessary to ensure * that none of the previous instructions in the same group are * affected by the rsm/ssm. */ +#include <asm-generic/barrier.h> + #endif /* _ASM_IA64_BARRIER_H */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:06 UTC
[PATCH v2 05/32] powerpc: reuse asm-generic/barrier.h
On powerpc read_barrier_depends, smp_read_barrier_depends smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/powerpc/include/asm/barrier.h | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h index a7af5fb..980ad0c 100644 --- a/arch/powerpc/include/asm/barrier.h +++ b/arch/powerpc/include/asm/barrier.h @@ -34,8 +34,6 @@ #define rmb() __asm__ __volatile__ ("sync" : : : "memory") #define wmb() __asm__ __volatile__ ("sync" : : : "memory") -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) - #ifdef __SUBARCH_HAS_LWSYNC # define SMPWMB LWSYNC #else @@ -60,9 +58,6 @@ #define smp_wmb() barrier() #endif /* CONFIG_SMP */ -#define read_barrier_depends() do { } while (0) -#define smp_read_barrier_depends() do { } while (0) - /* * This is a barrier which prevents following instructions from being * started until the value of the argument x is known. For example, if @@ -87,8 +82,8 @@ do { \ ___p1; \ }) -#define smp_mb__before_atomic() smp_mb() -#define smp_mb__after_atomic() smp_mb() #define smp_mb__before_spinlock() smp_mb() +#include <asm-generic/barrier.h> + #endif /* _ASM_POWERPC_BARRIER_H */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:06 UTC
[PATCH v2 06/32] s390: reuse asm-generic/barrier.h
On s390 read_barrier_depends, smp_read_barrier_depends smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/s390/include/asm/barrier.h | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h index 7ffd0b1..c358c31 100644 --- a/arch/s390/include/asm/barrier.h +++ b/arch/s390/include/asm/barrier.h @@ -30,14 +30,6 @@ #define smp_rmb() rmb() #define smp_wmb() wmb() -#define read_barrier_depends() do { } while (0) -#define smp_read_barrier_depends() do { } while (0) - -#define smp_mb__before_atomic() smp_mb() -#define smp_mb__after_atomic() smp_mb() - -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) - #define smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ @@ -53,4 +45,6 @@ do { \ ___p1; \ }) +#include <asm-generic/barrier.h> + #endif /* __ASM_BARRIER_H */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:06 UTC
[PATCH v2 07/32] sparc: reuse asm-generic/barrier.h
On sparc 64 bit dma_rmb, dma_wmb, smp_store_mb, smp_mb, smp_rmb, smp_wmb, read_barrier_depends and smp_read_barrier_depends match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. nop uses __asm__ __volatile but is otherwise identical to the generic version, drop that as well. This is in preparation to refactoring this code area. Note: nop() was in processor.h and not in barrier.h as on other architectures. Nothing seems to depend on it being there though. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/sparc/include/asm/barrier_32.h | 1 - arch/sparc/include/asm/barrier_64.h | 21 ++------------------- arch/sparc/include/asm/processor.h | 3 --- 3 files changed, 2 insertions(+), 23 deletions(-) diff --git a/arch/sparc/include/asm/barrier_32.h b/arch/sparc/include/asm/barrier_32.h index ae69eda..8059130 100644 --- a/arch/sparc/include/asm/barrier_32.h +++ b/arch/sparc/include/asm/barrier_32.h @@ -1,7 +1,6 @@ #ifndef __SPARC_BARRIER_H #define __SPARC_BARRIER_H -#include <asm/processor.h> /* for nop() */ #include <asm-generic/barrier.h> #endif /* !(__SPARC_BARRIER_H) */ diff --git a/arch/sparc/include/asm/barrier_64.h b/arch/sparc/include/asm/barrier_64.h index 14a9286..26c3f72 100644 --- a/arch/sparc/include/asm/barrier_64.h +++ b/arch/sparc/include/asm/barrier_64.h @@ -37,25 +37,6 @@ do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \ #define rmb() __asm__ __volatile__("":::"memory") #define wmb() __asm__ __volatile__("":::"memory") -#define dma_rmb() rmb() -#define dma_wmb() wmb() - -#define smp_store_mb(__var, __value) \ - do { WRITE_ONCE(__var, __value); membar_safe("#StoreLoad"); } while(0) - -#ifdef CONFIG_SMP -#define smp_mb() mb() -#define smp_rmb() rmb() -#define smp_wmb() wmb() -#else -#define smp_mb() __asm__ __volatile__("":::"memory") -#define smp_rmb() __asm__ __volatile__("":::"memory") -#define smp_wmb() __asm__ __volatile__("":::"memory") -#endif - -#define read_barrier_depends() do { } while (0) -#define smp_read_barrier_depends() do { } while (0) - #define smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ @@ -74,4 +55,6 @@ do { \ #define smp_mb__before_atomic() barrier() #define smp_mb__after_atomic() barrier() +#include <asm-generic/barrier.h> + #endif /* !(__SPARC64_BARRIER_H) */ diff --git a/arch/sparc/include/asm/processor.h b/arch/sparc/include/asm/processor.h index 2fe99e6..9da9646 100644 --- a/arch/sparc/include/asm/processor.h +++ b/arch/sparc/include/asm/processor.h @@ -5,7 +5,4 @@ #else #include <asm/processor_32.h> #endif - -#define nop() __asm__ __volatile__ ("nop") - #endif -- MST
Michael S. Tsirkin
2015-Dec-31 19:06 UTC
[PATCH v2 08/32] arm: reuse asm-generic/barrier.h
On arm smp_store_mb, read_barrier_depends, smp_read_barrier_depends, smp_store_release, smp_load_acquire, smp_mb__before_atomic and smp_mb__after_atomic match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/arm/include/asm/barrier.h | 23 +---------------------- 1 file changed, 1 insertion(+), 22 deletions(-) diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h index 3ff5642..31152e8 100644 --- a/arch/arm/include/asm/barrier.h +++ b/arch/arm/include/asm/barrier.h @@ -70,28 +70,7 @@ extern void arm_heavy_mb(void); #define smp_wmb() dmb(ishst) #endif -#define smp_store_release(p, v) \ -do { \ - compiletime_assert_atomic_type(*p); \ - smp_mb(); \ - WRITE_ONCE(*p, v); \ -} while (0) - -#define smp_load_acquire(p) \ -({ \ - typeof(*p) ___p1 = READ_ONCE(*p); \ - compiletime_assert_atomic_type(*p); \ - smp_mb(); \ - ___p1; \ -}) - -#define read_barrier_depends() do { } while(0) -#define smp_read_barrier_depends() do { } while(0) - -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) - -#define smp_mb__before_atomic() smp_mb() -#define smp_mb__after_atomic() smp_mb() +#include <asm-generic/barrier.h> #endif /* !__ASSEMBLY__ */ #endif /* __ASM_BARRIER_H */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:06 UTC
[PATCH v2 09/32] arm64: reuse asm-generic/barrier.h
On arm64 nop, read_barrier_depends, smp_read_barrier_depends smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/arm64/include/asm/barrier.h | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h index 9622eb4..91a43f4 100644 --- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -91,14 +91,7 @@ do { \ __u.__val; \ }) -#define read_barrier_depends() do { } while(0) -#define smp_read_barrier_depends() do { } while(0) - -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) -#define nop() asm volatile("nop"); - -#define smp_mb__before_atomic() smp_mb() -#define smp_mb__after_atomic() smp_mb() +#include <asm-generic/barrier.h> #endif /* __ASSEMBLY__ */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:07 UTC
[PATCH v2 10/32] metag: reuse asm-generic/barrier.h
On metag dma_rmb, dma_wmb, smp_store_mb, read_barrier_depends, smp_read_barrier_depends, smp_store_release and smp_load_acquire match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/metag/include/asm/barrier.h | 25 ++----------------------- 1 file changed, 2 insertions(+), 23 deletions(-) diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h index 172b7e5..b5b778b 100644 --- a/arch/metag/include/asm/barrier.h +++ b/arch/metag/include/asm/barrier.h @@ -44,9 +44,6 @@ static inline void wr_fence(void) #define rmb() barrier() #define wmb() mb() -#define dma_rmb() rmb() -#define dma_wmb() wmb() - #ifndef CONFIG_SMP #define fence() do { } while (0) #define smp_mb() barrier() @@ -81,27 +78,9 @@ static inline void fence(void) #endif #endif -#define read_barrier_depends() do { } while (0) -#define smp_read_barrier_depends() do { } while (0) - -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) - -#define smp_store_release(p, v) \ -do { \ - compiletime_assert_atomic_type(*p); \ - smp_mb(); \ - WRITE_ONCE(*p, v); \ -} while (0) - -#define smp_load_acquire(p) \ -({ \ - typeof(*p) ___p1 = READ_ONCE(*p); \ - compiletime_assert_atomic_type(*p); \ - smp_mb(); \ - ___p1; \ -}) - #define smp_mb__before_atomic() barrier() #define smp_mb__after_atomic() barrier() +#include <asm-generic/barrier.h> + #endif /* _ASM_METAG_BARRIER_H */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:07 UTC
[PATCH v2 11/32] mips: reuse asm-generic/barrier.h
On mips dma_rmb, dma_wmb, smp_store_mb, read_barrier_depends, smp_read_barrier_depends, smp_store_release and smp_load_acquire match the asm-generic variants exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/mips/include/asm/barrier.h | 25 ++----------------------- 1 file changed, 2 insertions(+), 23 deletions(-) diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h index 752e0b8..3eac4b9 100644 --- a/arch/mips/include/asm/barrier.h +++ b/arch/mips/include/asm/barrier.h @@ -10,9 +10,6 @@ #include <asm/addrspace.h> -#define read_barrier_depends() do { } while(0) -#define smp_read_barrier_depends() do { } while(0) - #ifdef CONFIG_CPU_HAS_SYNC #define __sync() \ __asm__ __volatile__( \ @@ -87,8 +84,6 @@ #define wmb() fast_wmb() #define rmb() fast_rmb() -#define dma_wmb() fast_wmb() -#define dma_rmb() fast_rmb() #if defined(CONFIG_WEAK_ORDERING) && defined(CONFIG_SMP) # ifdef CONFIG_CPU_CAVIUM_OCTEON @@ -112,9 +107,6 @@ #define __WEAK_LLSC_MB " \n" #endif -#define smp_store_mb(var, value) \ - do { WRITE_ONCE(var, value); smp_mb(); } while (0) - #define smp_llsc_mb() __asm__ __volatile__(__WEAK_LLSC_MB : : :"memory") #ifdef CONFIG_CPU_CAVIUM_OCTEON @@ -129,22 +121,9 @@ #define nudge_writes() mb() #endif -#define smp_store_release(p, v) \ -do { \ - compiletime_assert_atomic_type(*p); \ - smp_mb(); \ - WRITE_ONCE(*p, v); \ -} while (0) - -#define smp_load_acquire(p) \ -({ \ - typeof(*p) ___p1 = READ_ONCE(*p); \ - compiletime_assert_atomic_type(*p); \ - smp_mb(); \ - ___p1; \ -}) - #define smp_mb__before_atomic() smp_mb__before_llsc() #define smp_mb__after_atomic() smp_llsc_mb() +#include <asm-generic/barrier.h> + #endif /* __ASM_BARRIER_H */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:07 UTC
[PATCH v2 12/32] x86/um: reuse asm-generic/barrier.h
On x86/um CONFIG_SMP is never defined. As a result, several macros match the asm-generic variant exactly. Drop the local definitions and pull in asm-generic/barrier.h instead. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/x86/um/asm/barrier.h | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/arch/x86/um/asm/barrier.h b/arch/x86/um/asm/barrier.h index 755481f..174781a 100644 --- a/arch/x86/um/asm/barrier.h +++ b/arch/x86/um/asm/barrier.h @@ -36,13 +36,6 @@ #endif /* CONFIG_X86_PPRO_FENCE */ #define dma_wmb() barrier() -#define smp_mb() barrier() -#define smp_rmb() barrier() -#define smp_wmb() barrier() - -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0) - -#define read_barrier_depends() do { } while (0) -#define smp_read_barrier_depends() do { } while (0) +#include <asm-generic/barrier.h> #endif -- MST
Michael S. Tsirkin
2015-Dec-31 19:07 UTC
[PATCH v2 13/32] x86: reuse asm-generic/barrier.h
As on most architectures, on x86 read_barrier_depends and smp_read_barrier_depends are empty. Drop the local definitions and pull the generic ones from asm-generic/barrier.h instead: they are identical. This is in preparation to refactoring this code area. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/x86/include/asm/barrier.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index 0681d25..cc4c2a7 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -43,9 +43,6 @@ #define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0) #endif /* SMP */ -#define read_barrier_depends() do { } while (0) -#define smp_read_barrier_depends() do { } while (0) - #if defined(CONFIG_X86_PPRO_FENCE) /* @@ -91,4 +88,6 @@ do { \ #define smp_mb__before_atomic() barrier() #define smp_mb__after_atomic() barrier() +#include <asm-generic/barrier.h> + #endif /* _ASM_X86_BARRIER_H */ -- MST
Michael S. Tsirkin
2015-Dec-31 19:07 UTC
[PATCH v2 14/32] asm-generic: add __smp_xxx wrappers
On !SMP, most architectures define their barriers as compiler barriers. On SMP, most need an actual barrier. Make it possible to remove the code duplication for !SMP by defining low-level __smp_xxx barriers which do not depend on the value of SMP, then use them from asm-generic conditionally. Besides reducing code duplication, these low level APIs will also be useful for virtualization, where a barrier is sometimes needed even if !SMP since we might be talking to another kernel on the same SMP system. Both virtio and Xen drivers will benefit. The smp_xxx variants should use __smp_XXX ones or barrier() depending on SMP, identically for all architectures. We keep ifndef guards around them for now - once/if all architectures are converted to use the generic code, we'll be able to remove these. Suggested-by: Peter Zijlstra <peterz at infradead.org> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- include/asm-generic/barrier.h | 91 ++++++++++++++++++++++++++++++++++++++----- 1 file changed, 82 insertions(+), 9 deletions(-) diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index 987b2e0..8752964 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -54,22 +54,38 @@ #define read_barrier_depends() do { } while (0) #endif +#ifndef __smp_mb +#define __smp_mb() mb() +#endif + +#ifndef __smp_rmb +#define __smp_rmb() rmb() +#endif + +#ifndef __smp_wmb +#define __smp_wmb() wmb() +#endif + +#ifndef __smp_read_barrier_depends +#define __smp_read_barrier_depends() read_barrier_depends() +#endif + #ifdef CONFIG_SMP #ifndef smp_mb -#define smp_mb() mb() +#define smp_mb() __smp_mb() #endif #ifndef smp_rmb -#define smp_rmb() rmb() +#define smp_rmb() __smp_rmb() #endif #ifndef smp_wmb -#define smp_wmb() wmb() +#define smp_wmb() __smp_wmb() #endif #ifndef smp_read_barrier_depends -#define smp_read_barrier_depends() read_barrier_depends() +#define smp_read_barrier_depends() __smp_read_barrier_depends() #endif #else /* !CONFIG_SMP */ @@ -92,23 +108,78 @@ #endif /* CONFIG_SMP */ +#ifndef __smp_store_mb +#define __smp_store_mb(var, value) do { WRITE_ONCE(var, value); __smp_mb(); } while (0) +#endif + +#ifndef __smp_mb__before_atomic +#define __smp_mb__before_atomic() __smp_mb() +#endif + +#ifndef __smp_mb__after_atomic +#define __smp_mb__after_atomic() __smp_mb() +#endif + +#ifndef __smp_store_release +#define __smp_store_release(p, v) \ +do { \ + compiletime_assert_atomic_type(*p); \ + __smp_mb(); \ + WRITE_ONCE(*p, v); \ +} while (0) +#endif + +#ifndef __smp_load_acquire +#define __smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = READ_ONCE(*p); \ + compiletime_assert_atomic_type(*p); \ + __smp_mb(); \ + ___p1; \ +}) +#endif + +#ifdef CONFIG_SMP + +#ifndef smp_store_mb +#define smp_store_mb(var, value) __smp_store_mb(var, value) +#endif + +#ifndef smp_mb__before_atomic +#define smp_mb__before_atomic() __smp_mb__before_atomic() +#endif + +#ifndef smp_mb__after_atomic +#define smp_mb__after_atomic() __smp_mb__after_atomic() +#endif + +#ifndef smp_store_release +#define smp_store_release(p, v) __smp_store_release(p, v) +#endif + +#ifndef smp_load_acquire +#define smp_load_acquire(p) __smp_load_acquire(p) +#endif + +#else /* !CONFIG_SMP */ + #ifndef smp_store_mb -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0) #endif #ifndef smp_mb__before_atomic -#define smp_mb__before_atomic() smp_mb() +#define smp_mb__before_atomic() barrier() #endif #ifndef smp_mb__after_atomic -#define smp_mb__after_atomic() smp_mb() +#define smp_mb__after_atomic() barrier() #endif #ifndef smp_store_release #define smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ - smp_mb(); \ + barrier(); \ WRITE_ONCE(*p, v); \ } while (0) #endif @@ -118,10 +189,12 @@ do { \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ - smp_mb(); \ + barrier(); \ ___p1; \ }) #endif +#endif + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_GENERIC_BARRIER_H */ -- MST
This defines __smp_xxx barriers for powerpc for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h This reduces the amount of arch-specific boiler-plate code. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/powerpc/include/asm/barrier.h | 24 ++++++++---------------- 1 file changed, 8 insertions(+), 16 deletions(-) diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h index 980ad0c..c0deafc 100644 --- a/arch/powerpc/include/asm/barrier.h +++ b/arch/powerpc/include/asm/barrier.h @@ -44,19 +44,11 @@ #define dma_rmb() __lwsync() #define dma_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory") -#ifdef CONFIG_SMP -#define smp_lwsync() __lwsync() +#define __smp_lwsync() __lwsync() -#define smp_mb() mb() -#define smp_rmb() __lwsync() -#define smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory") -#else -#define smp_lwsync() barrier() - -#define smp_mb() barrier() -#define smp_rmb() barrier() -#define smp_wmb() barrier() -#endif /* CONFIG_SMP */ +#define __smp_mb() mb() +#define __smp_rmb() __lwsync() +#define __smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory") /* * This is a barrier which prevents following instructions from being @@ -67,18 +59,18 @@ #define data_barrier(x) \ asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory"); -#define smp_store_release(p, v) \ +#define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ - smp_lwsync(); \ + __smp_lwsync(); \ WRITE_ONCE(*p, v); \ } while (0) -#define smp_load_acquire(p) \ +#define __smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ - smp_lwsync(); \ + __smp_lwsync(); \ ___p1; \ }) -- MST
This defines __smp_xxx barriers for arm64, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Note: arm64 does not support !SMP config, so smp_xxx and __smp_xxx are always equivalent. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/arm64/include/asm/barrier.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h index 91a43f4..dae5c49 100644 --- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -35,11 +35,11 @@ #define dma_rmb() dmb(oshld) #define dma_wmb() dmb(oshst) -#define smp_mb() dmb(ish) -#define smp_rmb() dmb(ishld) -#define smp_wmb() dmb(ishst) +#define __smp_mb() dmb(ish) +#define __smp_rmb() dmb(ishld) +#define __smp_wmb() dmb(ishst) -#define smp_store_release(p, v) \ +#define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ switch (sizeof(*p)) { \ @@ -62,7 +62,7 @@ do { \ } \ } while (0) -#define smp_load_acquire(p) \ +#define __smp_load_acquire(p) \ ({ \ union { typeof(*p) __val; char __c[1]; } __u; \ compiletime_assert_atomic_type(*p); \ -- MST
This defines __smp_xxx barriers for arm, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h This reduces the amount of arch-specific boiler-plate code. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/arm/include/asm/barrier.h | 12 +++--------- 1 file changed, 3 insertions(+), 9 deletions(-) diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h index 31152e8..112cc1a 100644 --- a/arch/arm/include/asm/barrier.h +++ b/arch/arm/include/asm/barrier.h @@ -60,15 +60,9 @@ extern void arm_heavy_mb(void); #define dma_wmb() barrier() #endif -#ifndef CONFIG_SMP -#define smp_mb() barrier() -#define smp_rmb() barrier() -#define smp_wmb() barrier() -#else -#define smp_mb() dmb(ish) -#define smp_rmb() smp_mb() -#define smp_wmb() dmb(ishst) -#endif +#define __smp_mb() dmb(ish) +#define __smp_rmb() __smp_mb() +#define __smp_wmb() dmb(ishst) #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for blackfin, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/blackfin/include/asm/barrier.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/blackfin/include/asm/barrier.h b/arch/blackfin/include/asm/barrier.h index dfb66fe..7cca51c 100644 --- a/arch/blackfin/include/asm/barrier.h +++ b/arch/blackfin/include/asm/barrier.h @@ -78,8 +78,8 @@ #endif /* !CONFIG_SMP */ -#define smp_mb__before_atomic() barrier() -#define smp_mb__after_atomic() barrier() +#define __smp_mb__before_atomic() barrier() +#define __smp_mb__after_atomic() barrier() #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for ia64, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h This reduces the amount of arch-specific boiler-plate code. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Tony Luck <tony.luck at intel.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/ia64/include/asm/barrier.h | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h index 2f93348..588f161 100644 --- a/arch/ia64/include/asm/barrier.h +++ b/arch/ia64/include/asm/barrier.h @@ -42,28 +42,24 @@ #define dma_rmb() mb() #define dma_wmb() mb() -#ifdef CONFIG_SMP -# define smp_mb() mb() -#else -# define smp_mb() barrier() -#endif +# define __smp_mb() mb() -#define smp_mb__before_atomic() barrier() -#define smp_mb__after_atomic() barrier() +#define __smp_mb__before_atomic() barrier() +#define __smp_mb__after_atomic() barrier() /* * IA64 GCC turns volatile stores into st.rel and volatile loads into ld.acq no * need for asm trickery! */ -#define smp_store_release(p, v) \ +#define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ barrier(); \ WRITE_ONCE(*p, v); \ } while (0) -#define smp_load_acquire(p) \ +#define __smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ -- MST
This defines __smp_xxx barriers for metag, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Note: as __smp_XX macros should not depend on CONFIG_SMP, they can not use the existing fence() macro since that is defined differently between SMP and !SMP. For this reason, this patch introduces a wrapper metag_fence() that doesn't depend on CONFIG_SMP. fence() is then defined using that, depending on CONFIG_SMP. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/metag/include/asm/barrier.h | 32 +++++++++++++++----------------- 1 file changed, 15 insertions(+), 17 deletions(-) diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h index b5b778b..84880c9 100644 --- a/arch/metag/include/asm/barrier.h +++ b/arch/metag/include/asm/barrier.h @@ -44,13 +44,6 @@ static inline void wr_fence(void) #define rmb() barrier() #define wmb() mb() -#ifndef CONFIG_SMP -#define fence() do { } while (0) -#define smp_mb() barrier() -#define smp_rmb() barrier() -#define smp_wmb() barrier() -#else - #ifdef CONFIG_METAG_SMP_WRITE_REORDERING /* * Write to the atomic memory unlock system event register (command 0). This is @@ -60,26 +53,31 @@ static inline void wr_fence(void) * incoherence). It is therefore ineffective if used after and on the same * thread as a write. */ -static inline void fence(void) +static inline void metag_fence(void) { volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_ATOMIC_UNLOCK; barrier(); *flushptr = 0; barrier(); } -#define smp_mb() fence() -#define smp_rmb() fence() -#define smp_wmb() barrier() +#define __smp_mb() metag_fence() +#define __smp_rmb() metag_fence() +#define __smp_wmb() barrier() #else -#define fence() do { } while (0) -#define smp_mb() barrier() -#define smp_rmb() barrier() -#define smp_wmb() barrier() +#define metag_fence() do { } while (0) +#define __smp_mb() barrier() +#define __smp_rmb() barrier() +#define __smp_wmb() barrier() #endif + +#ifdef CONFIG_SMP +#define fence() metag_fence() +#else +#define fence() do { } while (0) #endif -#define smp_mb__before_atomic() barrier() -#define smp_mb__after_atomic() barrier() +#define __smp_mb__before_atomic() barrier() +#define __smp_mb__after_atomic() barrier() #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for mips, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Note: the only exception is smp_mb__before_llsc which is mips-specific. We define both the __smp_mb__before_llsc variant (for use in asm/barriers.h) and smp_mb__before_llsc (for use elsewhere on this architecture). Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/mips/include/asm/barrier.h | 26 ++++++++++++++------------ 1 file changed, 14 insertions(+), 12 deletions(-) diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h index 3eac4b9..d296633 100644 --- a/arch/mips/include/asm/barrier.h +++ b/arch/mips/include/asm/barrier.h @@ -85,20 +85,20 @@ #define wmb() fast_wmb() #define rmb() fast_rmb() -#if defined(CONFIG_WEAK_ORDERING) && defined(CONFIG_SMP) +#if defined(CONFIG_WEAK_ORDERING) # ifdef CONFIG_CPU_CAVIUM_OCTEON -# define smp_mb() __sync() -# define smp_rmb() barrier() -# define smp_wmb() __syncw() +# define __smp_mb() __sync() +# define __smp_rmb() barrier() +# define __smp_wmb() __syncw() # else -# define smp_mb() __asm__ __volatile__("sync" : : :"memory") -# define smp_rmb() __asm__ __volatile__("sync" : : :"memory") -# define smp_wmb() __asm__ __volatile__("sync" : : :"memory") +# define __smp_mb() __asm__ __volatile__("sync" : : :"memory") +# define __smp_rmb() __asm__ __volatile__("sync" : : :"memory") +# define __smp_wmb() __asm__ __volatile__("sync" : : :"memory") # endif #else -#define smp_mb() barrier() -#define smp_rmb() barrier() -#define smp_wmb() barrier() +#define __smp_mb() barrier() +#define __smp_rmb() barrier() +#define __smp_wmb() barrier() #endif #if defined(CONFIG_WEAK_REORDERING_BEYOND_LLSC) && defined(CONFIG_SMP) @@ -111,6 +111,7 @@ #ifdef CONFIG_CPU_CAVIUM_OCTEON #define smp_mb__before_llsc() smp_wmb() +#define __smp_mb__before_llsc() __smp_wmb() /* Cause previous writes to become visible on all CPUs as soon as possible */ #define nudge_writes() __asm__ __volatile__(".set push\n\t" \ ".set arch=octeon\n\t" \ @@ -118,11 +119,12 @@ ".set pop" : : : "memory") #else #define smp_mb__before_llsc() smp_llsc_mb() +#define __smp_mb__before_llsc() smp_llsc_mb() #define nudge_writes() mb() #endif -#define smp_mb__before_atomic() smp_mb__before_llsc() -#define smp_mb__after_atomic() smp_llsc_mb() +#define __smp_mb__before_atomic() __smp_mb__before_llsc() +#define __smp_mb__after_atomic() smp_llsc_mb() #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for s390, for use by virtualization. Some smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Note: smp_mb, smp_rmb and smp_wmb are defined as full barriers unconditionally on this architecture. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/s390/include/asm/barrier.h | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h index c358c31..fbd25b2 100644 --- a/arch/s390/include/asm/barrier.h +++ b/arch/s390/include/asm/barrier.h @@ -26,18 +26,21 @@ #define wmb() barrier() #define dma_rmb() mb() #define dma_wmb() mb() -#define smp_mb() mb() -#define smp_rmb() rmb() -#define smp_wmb() wmb() - -#define smp_store_release(p, v) \ +#define __smp_mb() mb() +#define __smp_rmb() rmb() +#define __smp_wmb() wmb() +#define smp_mb() __smp_mb() +#define smp_rmb() __smp_rmb() +#define smp_wmb() __smp_wmb() + +#define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ barrier(); \ WRITE_ONCE(*p, v); \ } while (0) -#define smp_load_acquire(p) \ +#define __smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ -- MST
Michael S. Tsirkin
2015-Dec-31 19:08 UTC
[PATCH v2 23/32] sh: define __smp_xxx, fix smp_store_mb for !SMP
sh variant of smp_store_mb() calls xchg() on !SMP which is stronger than implied by both the name and the documentation. define __smp_store_mb instead: code in asm-generic/barrier.h will then define smp_store_mb correctly depending on CONFIG_SMP. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/sh/include/asm/barrier.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/sh/include/asm/barrier.h b/arch/sh/include/asm/barrier.h index bf91037..f887c64 100644 --- a/arch/sh/include/asm/barrier.h +++ b/arch/sh/include/asm/barrier.h @@ -32,7 +32,8 @@ #define ctrl_barrier() __asm__ __volatile__ ("nop;nop;nop;nop;nop;nop;nop;nop") #endif -#define smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0) +#define __smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0) +#define smp_store_mb(var, value) __smp_store_mb(var, value) #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for sparc, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/sparc/include/asm/barrier_64.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/sparc/include/asm/barrier_64.h b/arch/sparc/include/asm/barrier_64.h index 26c3f72..c9f6ee6 100644 --- a/arch/sparc/include/asm/barrier_64.h +++ b/arch/sparc/include/asm/barrier_64.h @@ -37,14 +37,14 @@ do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \ #define rmb() __asm__ __volatile__("":::"memory") #define wmb() __asm__ __volatile__("":::"memory") -#define smp_store_release(p, v) \ +#define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ barrier(); \ WRITE_ONCE(*p, v); \ } while (0) -#define smp_load_acquire(p) \ +#define __smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ @@ -52,8 +52,8 @@ do { \ ___p1; \ }) -#define smp_mb__before_atomic() barrier() -#define smp_mb__after_atomic() barrier() +#define __smp_mb__before_atomic() barrier() +#define __smp_mb__after_atomic() barrier() #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for tile, for use by virtualization. Some smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Note: for 32 bit, keep smp_mb__after_atomic around since it's faster than the generic implementation. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/tile/include/asm/barrier.h | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/arch/tile/include/asm/barrier.h b/arch/tile/include/asm/barrier.h index 96a42ae..d552228 100644 --- a/arch/tile/include/asm/barrier.h +++ b/arch/tile/include/asm/barrier.h @@ -79,11 +79,12 @@ mb_incoherent(void) * But after the word is updated, the routine issues an "mf" before returning, * and since it's a function call, we don't even need a compiler barrier. */ -#define smp_mb__before_atomic() smp_mb() -#define smp_mb__after_atomic() do { } while (0) +#define __smp_mb__before_atomic() __smp_mb() +#define __smp_mb__after_atomic() do { } while (0) +#define smp_mb__after_atomic() __smp_mb__after_atomic() #else /* 64 bit */ -#define smp_mb__before_atomic() smp_mb() -#define smp_mb__after_atomic() smp_mb() +#define __smp_mb__before_atomic() __smp_mb() +#define __smp_mb__after_atomic() __smp_mb() #endif #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for xtensa, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/xtensa/include/asm/barrier.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/xtensa/include/asm/barrier.h b/arch/xtensa/include/asm/barrier.h index 5b88774..956596e 100644 --- a/arch/xtensa/include/asm/barrier.h +++ b/arch/xtensa/include/asm/barrier.h @@ -13,8 +13,8 @@ #define rmb() barrier() #define wmb() mb() -#define smp_mb__before_atomic() barrier() -#define smp_mb__after_atomic() barrier() +#define __smp_mb__before_atomic() barrier() +#define __smp_mb__after_atomic() barrier() #include <asm-generic/barrier.h> -- MST
This defines __smp_xxx barriers for x86, for use by virtualization. smp_xxx barriers are removed as they are defined correctly by asm-generic/barriers.h Signed-off-by: Michael S. Tsirkin <mst at redhat.com> Acked-by: Arnd Bergmann <arnd at arndb.de> --- arch/x86/include/asm/barrier.h | 31 ++++++++++++------------------- 1 file changed, 12 insertions(+), 19 deletions(-) diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index cc4c2a7..a584e1c 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -31,17 +31,10 @@ #endif #define dma_wmb() barrier() -#ifdef CONFIG_SMP -#define smp_mb() mb() -#define smp_rmb() dma_rmb() -#define smp_wmb() barrier() -#define smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0) -#else /* !SMP */ -#define smp_mb() barrier() -#define smp_rmb() barrier() -#define smp_wmb() barrier() -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0) -#endif /* SMP */ +#define __smp_mb() mb() +#define __smp_rmb() dma_rmb() +#define __smp_wmb() barrier() +#define __smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0) #if defined(CONFIG_X86_PPRO_FENCE) @@ -50,31 +43,31 @@ * model and we should fall back to full barriers. */ -#define smp_store_release(p, v) \ +#define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ - smp_mb(); \ + __smp_mb(); \ WRITE_ONCE(*p, v); \ } while (0) -#define smp_load_acquire(p) \ +#define __smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ - smp_mb(); \ + __smp_mb(); \ ___p1; \ }) #else /* regular x86 TSO memory ordering */ -#define smp_store_release(p, v) \ +#define __smp_store_release(p, v) \ do { \ compiletime_assert_atomic_type(*p); \ barrier(); \ WRITE_ONCE(*p, v); \ } while (0) -#define smp_load_acquire(p) \ +#define __smp_load_acquire(p) \ ({ \ typeof(*p) ___p1 = READ_ONCE(*p); \ compiletime_assert_atomic_type(*p); \ @@ -85,8 +78,8 @@ do { \ #endif /* Atomic operations are already serializing on x86 */ -#define smp_mb__before_atomic() barrier() -#define smp_mb__after_atomic() barrier() +#define __smp_mb__before_atomic() barrier() +#define __smp_mb__after_atomic() barrier() #include <asm-generic/barrier.h> -- MST
Michael S. Tsirkin
2015-Dec-31 19:09 UTC
[PATCH v2 28/32] asm-generic: implement virt_xxx memory barriers
Guests running within virtual machines might be affected by SMP effects even if the guest itself is compiled without SMP support. This is an artifact of interfacing with an SMP host while running an UP kernel. Using mandatory barriers for this use-case would be possible but is often suboptimal. In particular, virtio uses a bunch of confusing ifdefs to work around this, while xen just uses the mandatory barriers. To better handle this case, low-level virt_mb() etc macros are made available. These are implemented trivially using the low-level __smp_xxx macros, the purpose of these wrappers is to annotate those specific cases. These have the same effect as smp_mb() etc when SMP is enabled, but generate identical code for SMP and non-SMP systems. For example, virtual machine guests should use virt_mb() rather than smp_mb() when synchronizing against a (possibly SMP) host. Suggested-by: David Miller <davem at davemloft.net> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- include/asm-generic/barrier.h | 11 +++++++++++ Documentation/memory-barriers.txt | 28 +++++++++++++++++++++++----- 2 files changed, 34 insertions(+), 5 deletions(-) diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h index 8752964..1cceca14 100644 --- a/include/asm-generic/barrier.h +++ b/include/asm-generic/barrier.h @@ -196,5 +196,16 @@ do { \ #endif +/* Barriers for virtual machine guests when talking to an SMP host */ +#define virt_mb() __smp_mb() +#define virt_rmb() __smp_rmb() +#define virt_wmb() __smp_wmb() +#define virt_read_barrier_depends() __smp_read_barrier_depends() +#define virt_store_mb(var, value) __smp_store_mb(var, value) +#define virt_mb__before_atomic() __smp_mb__before_atomic() +#define virt_mb__after_atomic() __smp_mb__after_atomic() +#define virt_store_release(p, v) __smp_store_release(p, v) +#define virt_load_acquire(p) __smp_load_acquire(p) + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_GENERIC_BARRIER_H */ diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index aef9487..8f4a93a 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1655,17 +1655,18 @@ macro is a good place to start looking. SMP memory barriers are reduced to compiler barriers on uniprocessor compiled systems because it is assumed that a CPU will appear to be self-consistent, and will order overlapping accesses correctly with respect to itself. +However, see the subsection on "Virtual Machine Guests" below. [!] Note that SMP memory barriers _must_ be used to control the ordering of references to shared memory on SMP systems, though the use of locking instead is sufficient. Mandatory barriers should not be used to control SMP effects, since mandatory -barriers unnecessarily impose overhead on UP systems. They may, however, be -used to control MMIO effects on accesses through relaxed memory I/O windows. -These are required even on non-SMP systems as they affect the order in which -memory operations appear to a device by prohibiting both the compiler and the -CPU from reordering them. +barriers impose unnecessary overhead on both SMP and UP systems. They may, +however, be used to control MMIO effects on accesses through relaxed memory I/O +windows. These barriers are required even on non-SMP systems as they affect +the order in which memory operations appear to a device by prohibiting both the +compiler and the CPU from reordering them. There are some more advanced barrier functions: @@ -2948,6 +2949,23 @@ The Alpha defines the Linux kernel's memory barrier model. See the subsection on "Cache Coherency" above. +VIRTUAL MACHINE GUESTS +------------------- + +Guests running within virtual machines might be affected by SMP effects even if +the guest itself is compiled without SMP support. This is an artifact of +interfacing with an SMP host while running an UP kernel. Using mandatory +barriers for this use-case would be possible but is often suboptimal. + +To handle this case optimally, low-level virt_mb() etc macros are available. +These have the same effect as smp_mb() etc when SMP is enabled, but generate +identical code for SMP and non-SMP systems. For example, virtual machine guests +should use virt_mb() rather than smp_mb() when synchronizing against a +(possibly SMP) host. + +These are equivalent to smp_mb() etc counterparts in all other respects, +in particular, they do not control MMIO effects: to control +MMIO effects, use mandatory barriers. =========== EXAMPLE USES -- MST
Michael S. Tsirkin
2015-Dec-31 19:09 UTC
[PATCH v2 29/32] Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb"
This reverts commit 9e1a27ea42691429e31f158cce6fc61bc79bb2e9. While that commit optimizes !CONFIG_SMP, it mixes up DMA and SMP concepts, making the code hard to figure out. A better way to optimize this is with the new __smp_XXX barriers. As a first step, go back to full rmb/wmb barriers for !SMP. We switch to __smp_XXX barriers in the next patch. Cc: Peter Zijlstra <peterz at infradead.org> Cc: Alexander Duyck <alexander.duyck at gmail.com> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- include/linux/virtio_ring.h | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index 8e50888..67e06fe 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -21,20 +21,19 @@ * actually quite cheap. */ +#ifdef CONFIG_SMP static inline void virtio_mb(bool weak_barriers) { -#ifdef CONFIG_SMP if (weak_barriers) smp_mb(); else -#endif mb(); } static inline void virtio_rmb(bool weak_barriers) { if (weak_barriers) - dma_rmb(); + smp_rmb(); else rmb(); } @@ -42,10 +41,26 @@ static inline void virtio_rmb(bool weak_barriers) static inline void virtio_wmb(bool weak_barriers) { if (weak_barriers) - dma_wmb(); + smp_wmb(); else wmb(); } +#else +static inline void virtio_mb(bool weak_barriers) +{ + mb(); +} + +static inline void virtio_rmb(bool weak_barriers) +{ + rmb(); +} + +static inline void virtio_wmb(bool weak_barriers) +{ + wmb(); +} +#endif struct virtio_device; struct virtqueue; -- MST
Michael S. Tsirkin
2015-Dec-31 19:09 UTC
[PATCH v2 30/32] virtio_ring: update weak barriers to use __smp_XXX
virtio ring uses smp_wmb on SMP and wmb on !SMP, the reason for the later being that it might be talking to another kernel on the same SMP machine. This is exactly what __smp_XXX barriers do, so switch to these instead of homegrown ifdef hacks. Cc: Peter Zijlstra <peterz at infradead.org> Cc: Alexander Duyck <alexander.duyck at gmail.com> Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- include/linux/virtio_ring.h | 25 ++++--------------------- 1 file changed, 4 insertions(+), 21 deletions(-) diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index 67e06fe..f3fa55b 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -12,7 +12,7 @@ * anyone care? * * For virtio_pci on SMP, we don't need to order with respect to MMIO - * accesses through relaxed memory I/O windows, so smp_mb() et al are + * accesses through relaxed memory I/O windows, so virt_mb() et al are * sufficient. * * For using virtio to talk to real devices (eg. other heterogeneous @@ -21,11 +21,10 @@ * actually quite cheap. */ -#ifdef CONFIG_SMP static inline void virtio_mb(bool weak_barriers) { if (weak_barriers) - smp_mb(); + virt_mb(); else mb(); } @@ -33,7 +32,7 @@ static inline void virtio_mb(bool weak_barriers) static inline void virtio_rmb(bool weak_barriers) { if (weak_barriers) - smp_rmb(); + virt_rmb(); else rmb(); } @@ -41,26 +40,10 @@ static inline void virtio_rmb(bool weak_barriers) static inline void virtio_wmb(bool weak_barriers) { if (weak_barriers) - smp_wmb(); + virt_wmb(); else wmb(); } -#else -static inline void virtio_mb(bool weak_barriers) -{ - mb(); -} - -static inline void virtio_rmb(bool weak_barriers) -{ - rmb(); -} - -static inline void virtio_wmb(bool weak_barriers) -{ - wmb(); -} -#endif struct virtio_device; struct virtqueue; -- MST
Michael S. Tsirkin
2015-Dec-31 19:09 UTC
[PATCH v2 31/32] sh: support a 2-byte smp_store_mb
At the moment, xchg on sh only supports 4 and 1 byte values, so using it from smp_store_mb means attempts to store a 2 byte value using this macro fail. And happens to be exactly what virtio drivers want to do. Check size and fall back to a slower, but safe, WRITE_ONCE+smp_mb. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- arch/sh/include/asm/barrier.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/sh/include/asm/barrier.h b/arch/sh/include/asm/barrier.h index f887c64..0cc5735 100644 --- a/arch/sh/include/asm/barrier.h +++ b/arch/sh/include/asm/barrier.h @@ -32,7 +32,15 @@ #define ctrl_barrier() __asm__ __volatile__ ("nop;nop;nop;nop;nop;nop;nop;nop") #endif -#define __smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0) +#define __smp_store_mb(var, value) do { \ + if (sizeof(var) != 4 && sizeof(var) != 1) { \ + WRITE_ONCE(var, value); \ + __smp_mb(); \ + } else { \ + (void)xchg(&var, value); \ + } \ +} while (0) + #define smp_store_mb(var, value) __smp_store_mb(var, value) #include <asm-generic/barrier.h> -- MST
We need a full barrier after writing out event index, using virt_store_mb there seems better than open-coding. As usual, we need a wrapper to account for strong barriers. It's tempting to use this in vhost as well, for that, we'll need a variant of smp_store_mb that works on __user pointers. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- include/linux/virtio_ring.h | 12 ++++++++++++ drivers/virtio/virtio_ring.c | 15 +++++++++------ 2 files changed, 21 insertions(+), 6 deletions(-) diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index f3fa55b..3a74d91 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -45,6 +45,18 @@ static inline void virtio_wmb(bool weak_barriers) wmb(); } +static inline void virtio_store_mb(bool weak_barriers, + __virtio16 *p, __virtio16 v) +{ + if (weak_barriers) + virt_store_mb(*p, v); + else + { + WRITE_ONCE(*p, v); + mb(); + } +} + struct virtio_device; struct virtqueue; diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index ee663c4..e12e385 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -517,10 +517,10 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len) /* If we expect an interrupt for the next entry, tell host * by writing event index and flush out the write before * the read in the next get_buf call. */ - if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { - vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx); - virtio_mb(vq->weak_barriers); - } + if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) + virtio_store_mb(vq->weak_barriers, + &vring_used_event(&vq->vring), + cpu_to_virtio16(_vq->vdev, vq->last_used_idx)); #ifdef DEBUG vq->last_add_time_valid = false; @@ -653,8 +653,11 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) } /* TODO: tune this threshold */ bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4; - vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs); - virtio_mb(vq->weak_barriers); + + virtio_store_mb(vq->weak_barriers, + &vring_used_event(&vq->vring), + cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs)); + if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) - vq->last_used_idx) > bufs)) { END_USE(vq); return false; -- MST
drivers/xen/xenbus/xenbus_comms.c uses full memory barriers to communicate with the other side. For guests compiled with CONFIG_SMP, smp_wmb and smp_mb would be sufficient, so mb() and wmb() here are only needed if a non-SMP guest runs on an SMP host. Switch to virt_xxx barriers which serve this exact purpose. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- drivers/xen/xenbus/xenbus_comms.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c index fdb0f33..ecdecce 100644 --- a/drivers/xen/xenbus/xenbus_comms.c +++ b/drivers/xen/xenbus/xenbus_comms.c @@ -123,14 +123,14 @@ int xb_write(const void *data, unsigned len) avail = len; /* Must write data /after/ reading the consumer index. */ - mb(); + virt_mb(); memcpy(dst, data, avail); data += avail; len -= avail; /* Other side must not see new producer until data is there. */ - wmb(); + virt_wmb(); intf->req_prod += avail; /* Implies mb(): other side will see the updated producer. */ @@ -180,14 +180,14 @@ int xb_read(void *data, unsigned len) avail = len; /* Must read data /after/ reading the producer index. */ - rmb(); + virt_rmb(); memcpy(data, src, avail); data += avail; len -= avail; /* Other side must not see free space until we've copied out */ - mb(); + virt_mb(); intf->rsp_cons += avail; pr_debug("Finished read of %i bytes (%i to go)\n", avail, len); -- MST
include/xen/interface/io/ring.h uses full memory barriers to communicate with the other side. For guests compiled with CONFIG_SMP, smp_wmb and smp_mb would be sufficient, so mb() and wmb() here are only needed if a non-SMP guest runs on an SMP host. Switch to virt_xxx barriers which serve this exact purpose. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- include/xen/interface/io/ring.h | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h index 7dc685b..21f4fbd 100644 --- a/include/xen/interface/io/ring.h +++ b/include/xen/interface/io/ring.h @@ -208,12 +208,12 @@ struct __name##_back_ring { \ #define RING_PUSH_REQUESTS(_r) do { \ - wmb(); /* back sees requests /before/ updated producer index */ \ + virt_wmb(); /* back sees requests /before/ updated producer index */ \ (_r)->sring->req_prod = (_r)->req_prod_pvt; \ } while (0) #define RING_PUSH_RESPONSES(_r) do { \ - wmb(); /* front sees responses /before/ updated producer index */ \ + virt_wmb(); /* front sees responses /before/ updated producer index */ \ (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ } while (0) @@ -250,9 +250,9 @@ struct __name##_back_ring { \ #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ RING_IDX __old = (_r)->sring->req_prod; \ RING_IDX __new = (_r)->req_prod_pvt; \ - wmb(); /* back sees requests /before/ updated producer index */ \ + virt_wmb(); /* back sees requests /before/ updated producer index */ \ (_r)->sring->req_prod = __new; \ - mb(); /* back sees new requests /before/ we check req_event */ \ + virt_mb(); /* back sees new requests /before/ we check req_event */ \ (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ (RING_IDX)(__new - __old)); \ } while (0) @@ -260,9 +260,9 @@ struct __name##_back_ring { \ #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ RING_IDX __old = (_r)->sring->rsp_prod; \ RING_IDX __new = (_r)->rsp_prod_pvt; \ - wmb(); /* front sees responses /before/ updated producer index */ \ + virt_wmb(); /* front sees responses /before/ updated producer index */ \ (_r)->sring->rsp_prod = __new; \ - mb(); /* front sees new responses /before/ we check rsp_event */ \ + virt_mb(); /* front sees new responses /before/ we check rsp_event */ \ (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ (RING_IDX)(__new - __old)); \ } while (0) @@ -271,7 +271,7 @@ struct __name##_back_ring { \ (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ if (_work_to_do) break; \ (_r)->sring->req_event = (_r)->req_cons + 1; \ - mb(); \ + virt_mb(); \ (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ } while (0) @@ -279,7 +279,7 @@ struct __name##_back_ring { \ (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ if (_work_to_do) break; \ (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ - mb(); \ + virt_mb(); \ (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ } while (0) -- MST
From: "Michael S. Tsirkin" <mst at redhat.com> Date: Thu, 31 Dec 2015 21:06:38 +0200> On sparc 64 bit dma_rmb, dma_wmb, smp_store_mb, smp_mb, smp_rmb, > smp_wmb, read_barrier_depends and smp_read_barrier_depends match the > asm-generic variants exactly. Drop the local definitions and pull in > asm-generic/barrier.h instead. > > nop uses __asm__ __volatile but is otherwise identical to > the generic version, drop that as well. > > This is in preparation to refactoring this code area. > > Note: nop() was in processor.h and not in barrier.h as on other > architectures. Nothing seems to depend on it being there though. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de>Acked-by: David S. Miller <davem at davemloft.net>
From: "Michael S. Tsirkin" <mst at redhat.com> Date: Thu, 31 Dec 2015 21:08:53 +0200> This defines __smp_xxx barriers for sparc, > for use by virtualization. > > smp_xxx barriers are removed as they are > defined correctly by asm-generic/barriers.h > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de>Acked-by: David S. Miller <davem at davemloft.net>
Michael S. Tsirkin
2016-Jan-01 10:21 UTC
[PATCH v2 30/32] virtio_ring: update weak barriers to use __smp_xxx
On Fri, Jan 01, 2016 at 11:39:40AM +0200, Michael S. Tsirkin wrote:> virtio ring uses smp_wmb on SMP and wmb on !SMP, > the reason for the later being that it might be > talking to another kernel on the same SMP machine. > > This is exactly what __smp_XXX barriers do, > so switch to these instead of homegrown ifdef hacks. > > Cc: Peter Zijlstra <peterz at infradead.org> > Cc: Alexander Duyck <alexander.duyck at gmail.com> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>The subject and commit log should say virt_xxx and not __smp_xxx - I fixed this up in my tree.> --- > include/linux/virtio_ring.h | 25 ++++--------------------- > 1 file changed, 4 insertions(+), 21 deletions(-) > > diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h > index 67e06fe..f3fa55b 100644 > --- a/include/linux/virtio_ring.h > +++ b/include/linux/virtio_ring.h > @@ -12,7 +12,7 @@ > * anyone care? > * > * For virtio_pci on SMP, we don't need to order with respect to MMIO > - * accesses through relaxed memory I/O windows, so smp_mb() et al are > + * accesses through relaxed memory I/O windows, so virt_mb() et al are > * sufficient. > * > * For using virtio to talk to real devices (eg. other heterogeneous > @@ -21,11 +21,10 @@ > * actually quite cheap. > */ > > -#ifdef CONFIG_SMP > static inline void virtio_mb(bool weak_barriers) > { > if (weak_barriers) > - smp_mb(); > + virt_mb(); > else > mb(); > } > @@ -33,7 +32,7 @@ static inline void virtio_mb(bool weak_barriers) > static inline void virtio_rmb(bool weak_barriers) > { > if (weak_barriers) > - smp_rmb(); > + virt_rmb(); > else > rmb(); > } > @@ -41,26 +40,10 @@ static inline void virtio_rmb(bool weak_barriers) > static inline void virtio_wmb(bool weak_barriers) > { > if (weak_barriers) > - smp_wmb(); > + virt_wmb(); > else > wmb(); > } > -#else > -static inline void virtio_mb(bool weak_barriers) > -{ > - mb(); > -} > - > -static inline void virtio_rmb(bool weak_barriers) > -{ > - rmb(); > -} > - > -static inline void virtio_wmb(bool weak_barriers) > -{ > - wmb(); > -} > -#endif > > struct virtio_device; > struct virtqueue; > -- > MST
Hello. On 12/31/2015 10:09 PM, Michael S. Tsirkin wrote:> We need a full barrier after writing out event index, using > virt_store_mb there seems better than open-coding. As usual, we need a > wrapper to account for strong barriers. > > It's tempting to use this in vhost as well, for that, we'll > need a variant of smp_store_mb that works on __user pointers. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > --- > include/linux/virtio_ring.h | 12 ++++++++++++ > drivers/virtio/virtio_ring.c | 15 +++++++++------ > 2 files changed, 21 insertions(+), 6 deletions(-) > > diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h > index f3fa55b..3a74d91 100644 > --- a/include/linux/virtio_ring.h > +++ b/include/linux/virtio_ring.h > @@ -45,6 +45,18 @@ static inline void virtio_wmb(bool weak_barriers) > wmb(); > } > > +static inline void virtio_store_mb(bool weak_barriers, > + __virtio16 *p, __virtio16 v) > +{ > + if (weak_barriers) > + virt_store_mb(*p, v); > + else > + {The kernel coding style dictates: if (weak_barriers) { virt_store_mb(*p, v); } else {> + WRITE_ONCE(*p, v); > + mb(); > + } > +} > +[...] MBR, Sergei
Russell King - ARM Linux
2016-Jan-02 11:20 UTC
[PATCH v2 08/32] arm: reuse asm-generic/barrier.h
On Thu, Dec 31, 2015 at 09:06:46PM +0200, Michael S. Tsirkin wrote:> On arm smp_store_mb, read_barrier_depends, smp_read_barrier_depends, > smp_store_release, smp_load_acquire, smp_mb__before_atomic and > smp_mb__after_atomic match the asm-generic variants exactly. Drop the > local definitions and pull in asm-generic/barrier.h instead. > > This is in preparation to refactoring this code area. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de>Thanks, the asm-generic versions looks identical to me, so this should result in no code generation difference. Acked-by: Russell King <rmk+kernel at arm.linux.org.uk> -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
On Thu, Dec 31, 2015 at 09:07:59PM +0200, Michael S. Tsirkin wrote:> This defines __smp_xxx barriers for arm, > for use by virtualization. > > smp_xxx barriers are removed as they are > defined correctly by asm-generic/barriers.h > > This reduces the amount of arch-specific boiler-plate code. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de>In combination with patch 14, this looks like it should result in no change to the resulting code. Acked-by: Russell King <rmk+kernel at arm.linux.org.uk> My only concern is that it gives people an additional handle onto a "new" set of barriers - just because they're prefixed with __* unfortunately doesn't stop anyone from using it (been there with other arch stuff before.) I wonder whether we should consider making the smp memory barriers inline functions, so these __smp_xxx() variants can be undef'd afterwards, thereby preventing drivers getting their hands on these new macros? -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
David Vrabel
2016-Jan-04 11:32 UTC
[Xen-devel] [PATCH v2 33/34] xenbus: use virt_xxx barriers
On 31/12/15 19:10, Michael S. Tsirkin wrote:> drivers/xen/xenbus/xenbus_comms.c uses > full memory barriers to communicate with the other side. > > For guests compiled with CONFIG_SMP, smp_wmb and smp_mb > would be sufficient, so mb() and wmb() here are only needed if > a non-SMP guest runs on an SMP host. > > Switch to virt_xxx barriers which serve this exact purpose.Acked-by: David Vrabel <david.vrabel at citrix.com> If you're feeling particularly keen there's a rmb() consume_one_event() in drivers/xen/events/events_fifo.c that can be converted to virt_rmb() as well. David
David Vrabel
2016-Jan-04 11:32 UTC
[Xen-devel] [PATCH v2 34/34] xen/io: use virt_xxx barriers
On 31/12/15 19:10, Michael S. Tsirkin wrote:> include/xen/interface/io/ring.h uses > full memory barriers to communicate with the other side. > > For guests compiled with CONFIG_SMP, smp_wmb and smp_mb > would be sufficient, so mb() and wmb() here are only needed if > a non-SMP guest runs on an SMP host. > > Switch to virt_xxx barriers which serve this exact purpose.Acked-by: David Vrabel <david.vrabel at citrix.com> David
On Thu, 31 Dec 2015, Michael S. Tsirkin wrote:> drivers/xen/xenbus/xenbus_comms.c uses > full memory barriers to communicate with the other side. > > For guests compiled with CONFIG_SMP, smp_wmb and smp_mb > would be sufficient, so mb() and wmb() here are only needed if > a non-SMP guest runs on an SMP host. > > Switch to virt_xxx barriers which serve this exact purpose. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>Reviewed-by: Stefano Stabellini <stefano.stabellini at eu.citrix.com> Are you also going to take care of drivers/xen/grant-table.c drivers/xen/evtchn.c drivers/xen/events/events_fifo.c drivers/xen/xen-scsiback.c drivers/xen/tmem.c drivers/xen/xen-pciback/pci_stub.c drivers/xen/xen-pciback/pciback_ops.c ?> drivers/xen/xenbus/xenbus_comms.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c > index fdb0f33..ecdecce 100644 > --- a/drivers/xen/xenbus/xenbus_comms.c > +++ b/drivers/xen/xenbus/xenbus_comms.c > @@ -123,14 +123,14 @@ int xb_write(const void *data, unsigned len) > avail = len; > > /* Must write data /after/ reading the consumer index. */ > - mb(); > + virt_mb(); > > memcpy(dst, data, avail); > data += avail; > len -= avail; > > /* Other side must not see new producer until data is there. */ > - wmb(); > + virt_wmb(); > intf->req_prod += avail; > > /* Implies mb(): other side will see the updated producer. */ > @@ -180,14 +180,14 @@ int xb_read(void *data, unsigned len) > avail = len; > > /* Must read data /after/ reading the producer index. */ > - rmb(); > + virt_rmb(); > > memcpy(data, src, avail); > data += avail; > len -= avail; > > /* Other side must not see free space until we've copied out */ > - mb(); > + virt_mb(); > intf->rsp_cons += avail; > > pr_debug("Finished read of %i bytes (%i to go)\n", avail, len); > -- > MST >
On Thu, 31 Dec 2015, Michael S. Tsirkin wrote:> include/xen/interface/io/ring.h uses > full memory barriers to communicate with the other side. > > For guests compiled with CONFIG_SMP, smp_wmb and smp_mb > would be sufficient, so mb() and wmb() here are only needed if > a non-SMP guest runs on an SMP host. > > Switch to virt_xxx barriers which serve this exact purpose. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>Reviewed-by: Stefano Stabellini <stefano.stabellini at eu.citrix.com>> include/xen/interface/io/ring.h | 16 ++++++++-------- > 1 file changed, 8 insertions(+), 8 deletions(-) > > diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h > index 7dc685b..21f4fbd 100644 > --- a/include/xen/interface/io/ring.h > +++ b/include/xen/interface/io/ring.h > @@ -208,12 +208,12 @@ struct __name##_back_ring { \ > > > #define RING_PUSH_REQUESTS(_r) do { \ > - wmb(); /* back sees requests /before/ updated producer index */ \ > + virt_wmb(); /* back sees requests /before/ updated producer index */ \ > (_r)->sring->req_prod = (_r)->req_prod_pvt; \ > } while (0) > > #define RING_PUSH_RESPONSES(_r) do { \ > - wmb(); /* front sees responses /before/ updated producer index */ \ > + virt_wmb(); /* front sees responses /before/ updated producer index */ \ > (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \ > } while (0) > > @@ -250,9 +250,9 @@ struct __name##_back_ring { \ > #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \ > RING_IDX __old = (_r)->sring->req_prod; \ > RING_IDX __new = (_r)->req_prod_pvt; \ > - wmb(); /* back sees requests /before/ updated producer index */ \ > + virt_wmb(); /* back sees requests /before/ updated producer index */ \ > (_r)->sring->req_prod = __new; \ > - mb(); /* back sees new requests /before/ we check req_event */ \ > + virt_mb(); /* back sees new requests /before/ we check req_event */ \ > (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \ > (RING_IDX)(__new - __old)); \ > } while (0) > @@ -260,9 +260,9 @@ struct __name##_back_ring { \ > #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \ > RING_IDX __old = (_r)->sring->rsp_prod; \ > RING_IDX __new = (_r)->rsp_prod_pvt; \ > - wmb(); /* front sees responses /before/ updated producer index */ \ > + virt_wmb(); /* front sees responses /before/ updated producer index */ \ > (_r)->sring->rsp_prod = __new; \ > - mb(); /* front sees new responses /before/ we check rsp_event */ \ > + virt_mb(); /* front sees new responses /before/ we check rsp_event */ \ > (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \ > (RING_IDX)(__new - __old)); \ > } while (0) > @@ -271,7 +271,7 @@ struct __name##_back_ring { \ > (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ > if (_work_to_do) break; \ > (_r)->sring->req_event = (_r)->req_cons + 1; \ > - mb(); \ > + virt_mb(); \ > (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \ > } while (0) > > @@ -279,7 +279,7 @@ struct __name##_back_ring { \ > (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ > if (_work_to_do) break; \ > (_r)->sring->rsp_event = (_r)->rsp_cons + 1; \ > - mb(); \ > + virt_mb(); \ > (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \ > } while (0) > > -- > MST >
On Thu, Dec 31, 2015 at 09:06:30PM +0200, Michael S. Tsirkin wrote:> On s390 read_barrier_depends, smp_read_barrier_depends > smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the > asm-generic variants exactly. Drop the local definitions and pull in > asm-generic/barrier.h instead. > > This is in preparation to refactoring this code area. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de> > --- > arch/s390/include/asm/barrier.h | 10 ++-------- > 1 file changed, 2 insertions(+), 8 deletions(-) > > diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h > index 7ffd0b1..c358c31 100644 > --- a/arch/s390/include/asm/barrier.h > +++ b/arch/s390/include/asm/barrier.h > @@ -30,14 +30,6 @@ > #define smp_rmb() rmb() > #define smp_wmb() wmb() > > -#define read_barrier_depends() do { } while (0) > -#define smp_read_barrier_depends() do { } while (0) > - > -#define smp_mb__before_atomic() smp_mb() > -#define smp_mb__after_atomic() smp_mb()As per: lkml.kernel.org/r/20150921112252.3c2937e1 at mschwide s390 should change this to barrier() instead of smp_mb() and hence should not use the generic versions.
On Thu, Dec 31, 2015 at 09:07:10PM +0200, Michael S. Tsirkin wrote:> -#define smp_store_release(p, v) \ > -do { \ > - compiletime_assert_atomic_type(*p); \ > - smp_mb(); \ > - WRITE_ONCE(*p, v); \ > -} while (0) > - > -#define smp_load_acquire(p) \ > -({ \ > - typeof(*p) ___p1 = READ_ONCE(*p); \ > - compiletime_assert_atomic_type(*p); \ > - smp_mb(); \ > - ___p1; \ > -})David Daney wanted to use fancy new MIPS barriers to provide better implementations of this. This patch isn't in the way of that, just a FYI.
On Thu, Dec 31, 2015 at 09:08:22PM +0200, Michael S. Tsirkin wrote:> +#ifdef CONFIG_SMP > +#define fence() metag_fence() > +#else > +#define fence() do { } while (0) > #endifJames, it strikes me as odd that fence() is a no-op instead of a barrier() for UP, can you verify/explain?
On Thu, Dec 31, 2015 at 09:08:38PM +0200, Michael S. Tsirkin wrote:> This defines __smp_xxx barriers for s390, > for use by virtualization. > > Some smp_xxx barriers are removed as they are > defined correctly by asm-generic/barriers.h > > Note: smp_mb, smp_rmb and smp_wmb are defined as full barriers > unconditionally on this architecture. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de> > --- > arch/s390/include/asm/barrier.h | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h > index c358c31..fbd25b2 100644 > --- a/arch/s390/include/asm/barrier.h > +++ b/arch/s390/include/asm/barrier.h > @@ -26,18 +26,21 @@ > #define wmb() barrier() > #define dma_rmb() mb() > #define dma_wmb() mb() > -#define smp_mb() mb() > -#define smp_rmb() rmb() > -#define smp_wmb() wmb() > - > -#define smp_store_release(p, v) \ > +#define __smp_mb() mb() > +#define __smp_rmb() rmb() > +#define __smp_wmb() wmb() > +#define smp_mb() __smp_mb() > +#define smp_rmb() __smp_rmb() > +#define smp_wmb() __smp_wmb()Why define the smp_*mb() primitives here? Would not the inclusion of asm-generic/barrier.h do this?
On Thu, Dec 31, 2015 at 09:09:47PM +0200, Michael S. Tsirkin wrote:> At the moment, xchg on sh only supports 4 and 1 byte values, so using it > from smp_store_mb means attempts to store a 2 byte value using this > macro fail. > > And happens to be exactly what virtio drivers want to do. > > Check size and fall back to a slower, but safe, WRITE_ONCE+smp_mb. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > --- > arch/sh/include/asm/barrier.h | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/sh/include/asm/barrier.h b/arch/sh/include/asm/barrier.h > index f887c64..0cc5735 100644 > --- a/arch/sh/include/asm/barrier.h > +++ b/arch/sh/include/asm/barrier.h > @@ -32,7 +32,15 @@ > #define ctrl_barrier() __asm__ __volatile__ ("nop;nop;nop;nop;nop;nop;nop;nop") > #endif > > -#define __smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0) > +#define __smp_store_mb(var, value) do { \ > + if (sizeof(var) != 4 && sizeof(var) != 1) { \ > + WRITE_ONCE(var, value); \ > + __smp_mb(); \ > + } else { \ > + (void)xchg(&var, value); \ > + } \ > +} while (0)So SH is an orphaned arch, which is also why I did not comment on using xchg() for the UP smp_store_mb() thing. But I really think we should try fixing the xchg() implementation instead of this duct-tape.
On Thu, Dec 31, 2015 at 09:10:01PM +0200, Michael S. Tsirkin wrote:> drivers/xen/xenbus/xenbus_comms.c uses > full memory barriers to communicate with the other side. > > For guests compiled with CONFIG_SMP, smp_wmb and smp_mb > would be sufficient, so mb() and wmb() here are only needed if > a non-SMP guest runs on an SMP host. > > Switch to virt_xxx barriers which serve this exact purpose. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > --- > drivers/xen/xenbus/xenbus_comms.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c > index fdb0f33..ecdecce 100644 > --- a/drivers/xen/xenbus/xenbus_comms.c > +++ b/drivers/xen/xenbus/xenbus_comms.c > @@ -123,14 +123,14 @@ int xb_write(const void *data, unsigned len) > avail = len; > > /* Must write data /after/ reading the consumer index. */ > - mb(); > + virt_mb(); >So its possible to remove this barrier entirely, see the "CONTROL DEPENDNCIES" chunk of memory-barrier.txt. But do that in a separate patch series and only if you really really need the performance.
On Thu, Dec 31, 2015 at 09:07:02PM +0200, Michael S. Tsirkin wrote:> On metag dma_rmb, dma_wmb, smp_store_mb, read_barrier_depends, > smp_read_barrier_depends, smp_store_release and smp_load_acquire match > the asm-generic variants exactly. Drop the local definitions and pull in > asm-generic/barrier.h instead. > > This is in preparation to refactoring this code area. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de>Looks good, and confirmed no text change (once patch 1 is applied that is). Acked-by: James Hogan <james.hogan at imgtec.com> Thanks James> --- > arch/metag/include/asm/barrier.h | 25 ++----------------------- > 1 file changed, 2 insertions(+), 23 deletions(-) > > diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h > index 172b7e5..b5b778b 100644 > --- a/arch/metag/include/asm/barrier.h > +++ b/arch/metag/include/asm/barrier.h > @@ -44,9 +44,6 @@ static inline void wr_fence(void) > #define rmb() barrier() > #define wmb() mb() > > -#define dma_rmb() rmb() > -#define dma_wmb() wmb() > - > #ifndef CONFIG_SMP > #define fence() do { } while (0) > #define smp_mb() barrier() > @@ -81,27 +78,9 @@ static inline void fence(void) > #endif > #endif > > -#define read_barrier_depends() do { } while (0) > -#define smp_read_barrier_depends() do { } while (0) > - > -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0) > - > -#define smp_store_release(p, v) \ > -do { \ > - compiletime_assert_atomic_type(*p); \ > - smp_mb(); \ > - WRITE_ONCE(*p, v); \ > -} while (0) > - > -#define smp_load_acquire(p) \ > -({ \ > - typeof(*p) ___p1 = READ_ONCE(*p); \ > - compiletime_assert_atomic_type(*p); \ > - smp_mb(); \ > - ___p1; \ > -}) > - > #define smp_mb__before_atomic() barrier() > #define smp_mb__after_atomic() barrier() > > +#include <asm-generic/barrier.h> > + > #endif /* _ASM_METAG_BARRIER_H */ > -- > MST >-------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: <http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20160104/fd33fa53/attachment.sig>
Hi Michael, On Thu, Dec 31, 2015 at 09:08:22PM +0200, Michael S. Tsirkin wrote:> This defines __smp_xxx barriers for metag, > for use by virtualization. > > smp_xxx barriers are removed as they are > defined correctly by asm-generic/barriers.h > > Note: as __smp_XX macros should not depend on CONFIG_SMP, they can not > use the existing fence() macro since that is defined differently between > SMP and !SMP. For this reason, this patch introduces a wrapper > metag_fence() that doesn't depend on CONFIG_SMP. > fence() is then defined using that, depending on CONFIG_SMP.I'm not a fan of the inconsistent commit message wrapping. I wrap to 72 columns (although I now notice SubmittingPatches says to use 75...).> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de> > --- > arch/metag/include/asm/barrier.h | 32 +++++++++++++++----------------- > 1 file changed, 15 insertions(+), 17 deletions(-) > > diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h > index b5b778b..84880c9 100644 > --- a/arch/metag/include/asm/barrier.h > +++ b/arch/metag/include/asm/barrier.h > @@ -44,13 +44,6 @@ static inline void wr_fence(void) > #define rmb() barrier() > #define wmb() mb() > > -#ifndef CONFIG_SMP > -#define fence() do { } while (0) > -#define smp_mb() barrier() > -#define smp_rmb() barrier() > -#define smp_wmb() barrier() > -#else!SMP kernel text differs, but only because of new presence of unused metag_fence() inline function. If I #if 0 that out, then it matches, so thats fine.> - > #ifdef CONFIG_METAG_SMP_WRITE_REORDERING > /* > * Write to the atomic memory unlock system event register (command 0). This is > @@ -60,26 +53,31 @@ static inline void wr_fence(void) > * incoherence). It is therefore ineffective if used after and on the same > * thread as a write. > */ > -static inline void fence(void) > +static inline void metag_fence(void) > { > volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_ATOMIC_UNLOCK; > barrier(); > *flushptr = 0; > barrier(); > } > -#define smp_mb() fence() > -#define smp_rmb() fence() > -#define smp_wmb() barrier() > +#define __smp_mb() metag_fence() > +#define __smp_rmb() metag_fence() > +#define __smp_wmb() barrier() > #else > -#define fence() do { } while (0) > -#define smp_mb() barrier() > -#define smp_rmb() barrier() > -#define smp_wmb() barrier() > +#define metag_fence() do { } while (0) > +#define __smp_mb() barrier() > +#define __smp_rmb() barrier() > +#define __smp_wmb() barrier()Whitespace is now messed up. Admitedly its already inconsistent tabs/spaces, but it'd be nice if the definitions at least still all lined up. You're touching all the definitions which use spaces anyway, so feel free to convert them to tabs while you're at it. Other than those niggles, it looks sensible to me: Acked-by: James Hogan <james.hogan at imgtec.com> Cheers James> #endif > + > +#ifdef CONFIG_SMP > +#define fence() metag_fence() > +#else > +#define fence() do { } while (0) > #endif > > -#define smp_mb__before_atomic() barrier() > -#define smp_mb__after_atomic() barrier() > +#define __smp_mb__before_atomic() barrier() > +#define __smp_mb__after_atomic() barrier() > > #include <asm-generic/barrier.h> > > -- > MST >-------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: <http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20160105/822d84d1/attachment-0001.sig>
Hi Michael, On Thu, Dec 31, 2015 at 09:07:42PM +0200, Michael S. Tsirkin wrote:> This defines __smp_xxx barriers for powerpc > for use by virtualization. > > smp_xxx barriers are removed as they are > defined correctly by asm-generic/barriers.h > > This reduces the amount of arch-specific boiler-plate code. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de> > --- > arch/powerpc/include/asm/barrier.h | 24 ++++++++---------------- > 1 file changed, 8 insertions(+), 16 deletions(-) > > diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h > index 980ad0c..c0deafc 100644 > --- a/arch/powerpc/include/asm/barrier.h > +++ b/arch/powerpc/include/asm/barrier.h > @@ -44,19 +44,11 @@ > #define dma_rmb() __lwsync() > #define dma_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory") > > -#ifdef CONFIG_SMP > -#define smp_lwsync() __lwsync() > +#define __smp_lwsync() __lwsync() >so __smp_lwsync() is always mapped to lwsync, right?> -#define smp_mb() mb() > -#define smp_rmb() __lwsync() > -#define smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory") > -#else > -#define smp_lwsync() barrier() > - > -#define smp_mb() barrier() > -#define smp_rmb() barrier() > -#define smp_wmb() barrier() > -#endif /* CONFIG_SMP */ > +#define __smp_mb() mb() > +#define __smp_rmb() __lwsync() > +#define __smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory") > > /* > * This is a barrier which prevents following instructions from being > @@ -67,18 +59,18 @@ > #define data_barrier(x) \ > asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory"); > > -#define smp_store_release(p, v) \ > +#define __smp_store_release(p, v) \ > do { \ > compiletime_assert_atomic_type(*p); \ > - smp_lwsync(); \ > + __smp_lwsync(); \, therefore this will emit an lwsync no matter SMP or UP. Another thing is that smp_lwsync() may have a third user(other than smp_load_acquire() and smp_store_release()): http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877 I'm OK to change my patch accordingly, but do we really want smp_lwsync() get involved in this cleanup? If I understand you correctly, this cleanup focuses on external API like smp_{r,w,}mb(), while smp_lwsync() is internal to PPC. Regards, Boqun> WRITE_ONCE(*p, v); \ > } while (0) > > -#define smp_load_acquire(p) \ > +#define __smp_load_acquire(p) \ > ({ \ > typeof(*p) ___p1 = READ_ONCE(*p); \ > compiletime_assert_atomic_type(*p); \ > - smp_lwsync(); \ > + __smp_lwsync(); \ > ___p1; \ > }) > > -- > MST > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo at vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
Richard Weinberger
2016-Jan-05 23:12 UTC
[PATCH v2 12/32] x86/um: reuse asm-generic/barrier.h
Am 31.12.2015 um 20:07 schrieb Michael S. Tsirkin:> On x86/um CONFIG_SMP is never defined. As a result, several macros > match the asm-generic variant exactly. Drop the local definitions and > pull in asm-generic/barrier.h instead. > > This is in preparation to refactoring this code area. > > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Acked-by: Arnd Bergmann <arnd at arndb.de>Acked-by: Richard Weinberger <richard at nod.at> Thanks, //richard