This series replaces the existing paravirtualized spinlock mechanism
with a paravirtualized ticketlock mechanism. The series provides
implementation for both Xen and KVM.
The current set of patches are for Xen/x86 spinlock/KVM guest side, to be
included
against -tip.
I 'll be sending a separate patchset for KVM host based on kvm tree.
Please note I have added the below performance result (as suggested by HPA)
in the commit log of the first patch
Results:
======setup: 32 core machine with 32 vcpu KVM guest (HT off) with 8GB RAM
base = 3.11-rc
patched = base + pvspinlock V12
+-----------------+----------------+--------+
dbench (Throughput in MB/sec. Higher is better)
+-----------------+----------------+--------+
| base (stdev %)|patched(stdev%) | %gain |
+-----------------+----------------+--------+
| 15035.3 (0.3) |15150.0 (0.6) | 0.8 |
| 1470.0 (2.2) | 1713.7 (1.9) | 16.6 |
| 848.6 (4.3) | 967.8 (4.3) | 14.0 |
| 652.9 (3.5) | 685.3 (3.7) | 5.0 |
+-----------------+----------------+--------+
pvspinlock shows benefits for overcommit ratio > 1 for PLE enabled cases,
and undercommits results are flat.
non PLE results are much better for smaller VMs.
http://lkml.indiana.edu/hypermail/linux/kernel/1306.3/01095.html
I would thanks all the experts here for their time in reviewing and
commenting on the patch series (including perhaps who have been not
listed).
Finally special thanks to KVM maintainers (Avi, Marcelo, Gleb) for
their comments and Andrew Theurer, Chegu Vinod for their valuable
testing and feedback.
The older series[4] was tested by Attilio for Xen implementation.
Note that Konrad needs to revert below two patches to enable xen on hvm
70dd4998, f10cd522c
Changes in V12
- spiltted uapi header patch.
- dropped patch 18.
- bailout of lock spinning in case of NMI (Gleb)
- drop out patch 18 whose benefits are inconclusive (Gleb, Ingo)
Changes in V11:
- use safe_halt in lock_spinning path to avoid potential problem
in case of irq_handlers taking lock in slowpath (Gleb)
- add a0 flag for the kick hypercall for future extension (Gleb)
- add stubs for missing architecture for kvm_vcpu_schedule() (Gleb)
- Change hypercall documentation.
- Rebased to 3.11-rc1
Changes in V10:
Addressed Konrad's review comments:
- Added break in patch 5 since now we know exact cpu to wakeup
- Dropped patch 12 and Konrad needs to revert two patches to enable xen on hvm
70dd4998, f10cd522c
- Remove TIMEOUT and corrected spacing in patch 15
- Kicked spelling and correct spacing in patches 17, 18
Changes in V9:
- Changed spin_threshold to 32k to avoid excess halt exits that are
causing undercommit degradation (after PLE handler improvement).
- Added kvm_irq_delivery_to_apic (suggested by Gleb)
- Optimized halt exit path to use PLE handler
V8 of PVspinlock was posted last year. After Avi's suggestions to look
at PLE handler's improvements, various optimizations in PLE handling
have been tried.
With this series we see that we could get little more improvements on top
of that.
Changes before V8:
Ticketlock change history:
Changes in V7:
- Reabsed patches to 3.4-rc3
- Added jumplabel split patch (originally from Andrew Jones rebased to
3.4-rc3
- jumplabel changes from Ingo and Jason taken and now using static_key_*
instead of static_branch.
- using UNINLINE_SPIN_UNLOCK (which was splitted as per suggestion from Linus)
- This patch series is rebased on debugfs patch (that sould be already in
Xen/linux-next https://lkml.org/lkml/2012/3/23/51)
Changes in V6 posting: (Raghavendra K T)
- Rebased to linux-3.3-rc6.
- used function+enum in place of macro (better type checking)
- use cmpxchg while resetting zero status for possible race
[suggested by Dave Hansen for KVM patches ]
KVM patch Change history:
Changes in V6:
- Rebased to 3.4-rc3
- Removed debugfs changes patch which should now be in Xen/linux-next.
(https://lkml.org/lkml/2012/3/30/687)
- Removed PV_UNHALT_MSR since currently we don't need guest communication,
and made pv_unhalt folded to GET_MP_STATE (Marcello, Avi[long back])
- Take jumplabel changes from Ingo/Jason into use (static_key_slow_inc usage)
- Added inline to spinlock_init in non PARAVIRT case
- Move arch specific code to arch/x86 and add stubs to other archs (Marcello)
- Added more comments on pv_unhalt usage etc (Marcello)
Changes in V5:
- rebased to 3.3-rc6
- added PV_UNHALT_MSR that would help in live migration (Avi)
- removed PV_LOCK_KICK vcpu request and pv_unhalt flag (re)added.
- Changed hypercall documentaion (Alex).
- mode_t changed to umode_t in debugfs.
- MSR related documentation added.
- rename PV_LOCK_KICK to PV_UNHALT.
- host and guest patches not mixed. (Marcelo, Alex)
- kvm_kick_cpu now takes cpu so it can be used by flush_tlb_ipi_other
paravirtualization (Nikunj)
- coding style changes in variable declarion etc (Srikar)
Changes in V4:
- reabsed to 3.2.0 pre.
- use APIC ID for kicking the vcpu and use kvm_apic_match_dest for matching
(Avi)
- fold vcpu->kicked flag into vcpu->requests (KVM_REQ_PVLOCK_KICK) and
related
changes for UNHALT path to make pv ticket spinlock migration friendly(Avi,
Marcello)
- Added Documentation for CPUID, Hypercall (KVM_HC_KICK_CPU)
and capabilty (KVM_CAP_PVLOCK_KICK) (Avi)
- Remove unneeded kvm_arch_vcpu_ioctl_set_mpstate call. (Marcello)
- cumulative variable type changed (int ==> u32) in add_stat (Konrad)
- remove unneeded kvm_guest_init for !CONFIG_KVM_GUEST case
Changes in V3:
- rebased to 3.2-rc1
- use halt() instead of wait for kick hypercall.
- modify kick hyper call to do wakeup halted vcpu.
- hook kvm_spinlock_init to smp_prepare_cpus call (moved the call out of
head##.c).
- fix the potential race when zero_stat is read.
- export debugfs_create_32 and add documentation to API.
- use static inline and enum instead of ADDSTAT macro.
- add barrier() in after setting kick_vcpu.
- empty static inline function for kvm_spinlock_init.
- combine the patches one and two readuce overhead.
- make KVM_DEBUGFS depends on DEBUGFS.
- include debugfs header unconditionally.
Changes in V2:
- rebased patchesto -rc9
- synchronization related changes based on Jeremy's changes
(Jeremy Fitzhardinge <jeremy.fitzhardinge at citrix.com>) pointed by
Stephan Diestelhorst <stephan.diestelhorst at amd.com>
- enabling 32 bit guests
- splitted patches into two more chunks
Description:
Ticket locks have an inherent problem in a virtualized case, because
the vCPUs are scheduled rather than running concurrently (ignoring
gang scheduled vCPUs). This can result in catastrophic performance
collapses when the vCPU scheduler doesn't schedule the correct
"next"
vCPU, and ends up scheduling a vCPU which burns its entire timeslice
spinning. (Note that this is not the same problem as lock-holder
preemption, which this series also addresses; that's also a problem,
but not catastrophic).
(See Thomas Friebel's talk "Prevent Guests from Spinning Around"
http://www.xen.org/files/xensummitboston08/LHP.pdf for more details.)
Currently we deal with this by having PV spinlocks, which adds a layer
of indirection in front of all the spinlock functions, and defining a
completely new implementation for Xen (and for other pvops users, but
there are none at present).
PV ticketlocks keeps the existing ticketlock implemenentation
(fastpath) as-is, but adds a couple of pvops for the slow paths:
- If a CPU has been waiting for a spinlock for SPIN_THRESHOLD
iterations, then call out to the __ticket_lock_spinning() pvop,
which allows a backend to block the vCPU rather than spinning. This
pvop can set the lock into "slowpath state".
- When releasing a lock, if it is in "slowpath state", the call
__ticket_unlock_kick() to kick the next vCPU in line awake. If the
lock is no longer in contention, it also clears the slowpath flag.
The "slowpath state" is stored in the LSB of the within the lock tail
ticket. This has the effect of reducing the max number of CPUs by
half (so, a "small ticket" can deal with 128 CPUs, and "large
ticket"
32768).
For KVM, one hypercall is introduced in hypervisor,that allows a vcpu to kick
another vcpu out of halt state.
The blocking of vcpu is done using halt() in (lock_spinning) slowpath.
Overall, it results in a large reduction in code, it makes the native
and virtualized cases closer, and it removes a layer of indirection
around all the spinlock functions.
The fast path (taking an uncontended lock which isn't in
"slowpath"
state) is optimal, identical to the non-paravirtualized case.
The inner part of ticket lock code becomes:
inc = xadd(&lock->tickets, inc);
inc.tail &= ~TICKET_SLOWPATH_FLAG;
if (likely(inc.head == inc.tail))
goto out;
for (;;) {
unsigned count = SPIN_THRESHOLD;
do {
if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
goto out;
cpu_relax();
} while (--count);
__ticket_lock_spinning(lock, inc.tail);
}
out: barrier();
which results in:
push %rbp
mov %rsp,%rbp
mov $0x200,%eax
lock xadd %ax,(%rdi)
movzbl %ah,%edx
cmp %al,%dl
jne 1f # Slowpath if lock in contention
pop %rbp
retq
### SLOWPATH START
1: and $-2,%edx
movzbl %dl,%esi
2: mov $0x800,%eax
jmp 4f
3: pause
sub $0x1,%eax
je 5f
4: movzbl (%rdi),%ecx
cmp %cl,%dl
jne 3b
pop %rbp
retq
5: callq *__ticket_lock_spinning
jmp 2b
### SLOWPATH END
with CONFIG_PARAVIRT_SPINLOCKS=n, the code has changed slightly, where
the fastpath case is straight through (taking the lock without
contention), and the spin loop is out of line:
push %rbp
mov %rsp,%rbp
mov $0x100,%eax
lock xadd %ax,(%rdi)
movzbl %ah,%edx
cmp %al,%dl
jne 1f
pop %rbp
retq
### SLOWPATH START
1: pause
movzbl (%rdi),%eax
cmp %dl,%al
jne 1b
pop %rbp
retq
### SLOWPATH END
The unlock code is complicated by the need to both add to the lock's
"head" and fetch the slowpath flag from "tail". This
version of the
patch uses a locked add to do this, followed by a test to see if the
slowflag is set. The lock prefix acts as a full memory barrier, so we
can be sure that other CPUs will have seen the unlock before we read
the flag (without the barrier the read could be fetched from the
store queue before it hits memory, which could result in a deadlock).
This is is all unnecessary complication if you're not using PV ticket
locks, it also uses the jump-label machinery to use the standard
"add"-based unlock in the non-PV case.
if (TICKET_SLOWPATH_FLAG &&
static_key_false(¶virt_ticketlocks_enabled))) {
arch_spinlock_t prev;
prev = *lock;
add_smp(&lock->tickets.head, TICKET_LOCK_INC);
/* add_smp() is a full mb() */
if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
__ticket_unlock_slowpath(lock, prev);
} else
__add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
which generates:
push %rbp
mov %rsp,%rbp
nop5 # replaced by 5-byte jmp 2f when PV enabled
# non-PV unlock
addb $0x2,(%rdi)
1: pop %rbp
retq
### PV unlock ###
2: movzwl (%rdi),%esi # Fetch prev
lock addb $0x2,(%rdi) # Do unlock
testb $0x1,0x1(%rdi) # Test flag
je 1b # Finished if not set
### Slow path ###
add $2,%sil # Add "head" in old lock state
mov %esi,%edx
and $0xfe,%dh # clear slowflag for comparison
movzbl %dh,%eax
cmp %dl,%al # If head == tail (uncontended)
je 4f # clear slowpath flag
# Kick next CPU waiting for lock
3: movzbl %sil,%esi
callq *pv_lock_ops.kick
pop %rbp
retq
# Lock no longer contended - clear slowflag
4: mov %esi,%eax
lock cmpxchg %dx,(%rdi) # cmpxchg to clear flag
cmp %si,%ax
jne 3b # If clear failed, then kick
pop %rbp
retq
So when not using PV ticketlocks, the unlock sequence just has a
5-byte nop added to it, and the PV case is reasonable straightforward
aside from requiring a "lock add".
Jeremy Fitzhardinge (9):
x86/spinlock: Replace pv spinlocks with pv ticketlocks
x86/ticketlock: Collapse a layer of functions
xen: Defer spinlock setup until boot CPU setup
xen/pvticketlock: Xen implementation for PV ticket locks
xen/pvticketlocks: Add xen_nopvspin parameter to disable xen pv ticketlocks
x86/pvticketlock: Use callee-save for lock_spinning
x86/pvticketlock: When paravirtualizing ticket locks, increment by 2
x86/ticketlock: Add slowpath logic
xen/pvticketlock: Allow interrupts to be enabled while blocking
Andrew Jones (1):
jump_label: Split jumplabel ratelimit
Srivatsa Vaddagiri (2):
kvm guest : Add configuration support to enable debug information for KVM
Guests
kvm : Paravirtual ticketlocks support for linux guests running on KVM
hypervisor
Raghavendra K T (2):
x86/ticketlock: Don't inline _spin_unlock when using paravirt spinlocks
kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi
---
[1]. V11 PV Ticketspinlock for Xen/KVM link: https://lkml.org/lkml/2013/7/22/29
[2]. V10 PV Ticketspinlock for Xen/KVM link: https://lkml.org/lkml/2013/6/24/252
[3]. V9 PV Ticketspinlock for Xen/KVM link: https://lkml.org/lkml/2013/6/1/168
[4]. V8 PV Ticketspinlock for Xen/KVM link: https://lkml.org/lkml/2012/5/2/119
arch/x86/Kconfig | 10 +
arch/x86/include/asm/kvm_para.h | 14 +-
arch/x86/include/asm/paravirt.h | 32 +--
arch/x86/include/asm/paravirt_types.h | 10 +-
arch/x86/include/asm/spinlock.h | 128 +++++++----
arch/x86/include/asm/spinlock_types.h | 16 +-
arch/x86/include/uapi/asm/kvm_para.h | 1 +
arch/x86/kernel/kvm.c | 262 +++++++++++++++++++++++
arch/x86/kernel/paravirt-spinlocks.c | 18 +-
arch/x86/xen/smp.c | 2 +-
arch/x86/xen/spinlock.c | 387 +++++++++++-----------------------
include/linux/jump_label.h | 26 +--
include/linux/jump_label_ratelimit.h | 34 +++
include/linux/perf_event.h | 1 +
include/uapi/linux/kvm_para.h | 1 +
kernel/jump_label.c | 1 +
16 files changed, 565 insertions(+), 378 deletions(-)
Raghavendra K T
2013-Aug-06 11:40 UTC
[PATCH V12 1/14] x86/spinlock: Replace pv spinlocks with pv ticketlocks
x86/spinlock: Replace pv spinlocks with pv ticketlocks
From: Jeremy Fitzhardinge <jeremy at goop.org>
Rather than outright replacing the entire spinlock implementation in
order to paravirtualize it, keep the ticket lock implementation but add
a couple of pvops hooks on the slow patch (long spin on lock, unlocking
a contended lock).
Ticket locks have a number of nice properties, but they also have some
surprising behaviours in virtual environments. They enforce a strict
FIFO ordering on cpus trying to take a lock; however, if the hypervisor
scheduler does not schedule the cpus in the correct order, the system can
waste a huge amount of time spinning until the next cpu can take the lock.
(See Thomas Friebel's talk "Prevent Guests from Spinning Around"
http://www.xen.org/files/xensummitboston08/LHP.pdf for more details.)
To address this, we add two hooks:
- __ticket_spin_lock which is called after the cpu has been
spinning on the lock for a significant number of iterations but has
failed to take the lock (presumably because the cpu holding the lock
has been descheduled). The lock_spinning pvop is expected to block
the cpu until it has been kicked by the current lock holder.
- __ticket_spin_unlock, which on releasing a contended lock
(there are more cpus with tail tickets), it looks to see if the next
cpu is blocked and wakes it if so.
When compiled with CONFIG_PARAVIRT_SPINLOCKS disabled, a set of stub
functions causes all the extra code to go away.
Results:
======setup: 32 core machine with 32 vcpu KVM guest (HT off) with 8GB RAM
base = 3.11-rc
patched = base + pvspinlock V12
+-----------------+----------------+--------+
dbench (Throughput in MB/sec. Higher is better)
+-----------------+----------------+--------+
| base (stdev %)|patched(stdev%) | %gain |
+-----------------+----------------+--------+
| 15035.3 (0.3) |15150.0 (0.6) | 0.8 |
| 1470.0 (2.2) | 1713.7 (1.9) | 16.6 |
| 848.6 (4.3) | 967.8 (4.3) | 14.0 |
| 652.9 (3.5) | 685.3 (3.7) | 5.0 |
+-----------------+----------------+--------+
pvspinlock shows benefits for overcommit ratio > 1 for PLE enabled cases,
and undercommits results are flat
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Tested-by: Attilio Rao <attilio.rao at citrix.com>
[ Raghavendra: Changed SPIN_THRESHOLD ]
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/include/asm/paravirt.h | 32 ++++----------------
arch/x86/include/asm/paravirt_types.h | 10 ++----
arch/x86/include/asm/spinlock.h | 53 +++++++++++++++++++++++++++------
arch/x86/include/asm/spinlock_types.h | 4 --
arch/x86/kernel/paravirt-spinlocks.c | 15 +--------
arch/x86/xen/spinlock.c | 8 ++++-
6 files changed, 61 insertions(+), 61 deletions(-)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index cfdc9ee..040e72d 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -712,36 +712,16 @@ static inline void __set_fixmap(unsigned /* enum
fixed_addresses */ idx,
#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT_SPINLOCKS)
-static inline int arch_spin_is_locked(struct arch_spinlock *lock)
+static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
+ __ticket_t ticket)
{
- return PVOP_CALL1(int, pv_lock_ops.spin_is_locked, lock);
+ PVOP_VCALL2(pv_lock_ops.lock_spinning, lock, ticket);
}
-static inline int arch_spin_is_contended(struct arch_spinlock *lock)
+static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
+ __ticket_t ticket)
{
- return PVOP_CALL1(int, pv_lock_ops.spin_is_contended, lock);
-}
-#define arch_spin_is_contended arch_spin_is_contended
-
-static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
-{
- PVOP_VCALL1(pv_lock_ops.spin_lock, lock);
-}
-
-static __always_inline void arch_spin_lock_flags(struct arch_spinlock *lock,
- unsigned long flags)
-{
- PVOP_VCALL2(pv_lock_ops.spin_lock_flags, lock, flags);
-}
-
-static __always_inline int arch_spin_trylock(struct arch_spinlock *lock)
-{
- return PVOP_CALL1(int, pv_lock_ops.spin_trylock, lock);
-}
-
-static __always_inline void arch_spin_unlock(struct arch_spinlock *lock)
-{
- PVOP_VCALL1(pv_lock_ops.spin_unlock, lock);
+ PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
}
#endif
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 0db1fca..d5deb6d 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -327,13 +327,11 @@ struct pv_mmu_ops {
};
struct arch_spinlock;
+#include <asm/spinlock_types.h>
+
struct pv_lock_ops {
- int (*spin_is_locked)(struct arch_spinlock *lock);
- int (*spin_is_contended)(struct arch_spinlock *lock);
- void (*spin_lock)(struct arch_spinlock *lock);
- void (*spin_lock_flags)(struct arch_spinlock *lock, unsigned long flags);
- int (*spin_trylock)(struct arch_spinlock *lock);
- void (*spin_unlock)(struct arch_spinlock *lock);
+ void (*lock_spinning)(struct arch_spinlock *lock, __ticket_t ticket);
+ void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
};
/* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 33692ea..4d54244 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -34,6 +34,35 @@
# define UNLOCK_LOCK_PREFIX
#endif
+/* How long a lock should spin before we consider blocking */
+#define SPIN_THRESHOLD (1 << 15)
+
+#ifndef CONFIG_PARAVIRT_SPINLOCKS
+
+static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
+ __ticket_t ticket)
+{
+}
+
+static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
+ __ticket_t ticket)
+{
+}
+
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+
+
+/*
+ * If a spinlock has someone waiting on it, then kick the appropriate
+ * waiting cpu.
+ */
+static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
+ __ticket_t next)
+{
+ if (unlikely(lock->tickets.tail != next))
+ ____ticket_unlock_kick(lock, next);
+}
+
/*
* Ticket locks are conceptually two parts, one indicating the current head of
* the queue, and the other indicating the current tail. The lock is acquired
@@ -47,19 +76,24 @@
* in the high part, because a wide xadd increment of the low part would carry
* up and contaminate the high part.
*/
-static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
+static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
{
register struct __raw_tickets inc = { .tail = 1 };
inc = xadd(&lock->tickets, inc);
for (;;) {
- if (inc.head == inc.tail)
- break;
- cpu_relax();
- inc.head = ACCESS_ONCE(lock->tickets.head);
+ unsigned count = SPIN_THRESHOLD;
+
+ do {
+ if (inc.head == inc.tail)
+ goto out;
+ cpu_relax();
+ inc.head = ACCESS_ONCE(lock->tickets.head);
+ } while (--count);
+ __ticket_lock_spinning(lock, inc.tail);
}
- barrier(); /* make sure nothing creeps before the lock is taken */
+out: barrier(); /* make sure nothing creeps before the lock is taken */
}
static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
@@ -78,7 +112,10 @@ static __always_inline int
__ticket_spin_trylock(arch_spinlock_t *lock)
static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
{
+ __ticket_t next = lock->tickets.head + 1;
+
__add(&lock->tickets.head, 1, UNLOCK_LOCK_PREFIX);
+ __ticket_unlock_kick(lock, next);
}
static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
@@ -95,8 +132,6 @@ static inline int __ticket_spin_is_contended(arch_spinlock_t
*lock)
return (__ticket_t)(tmp.tail - tmp.head) > 1;
}
-#ifndef CONFIG_PARAVIRT_SPINLOCKS
-
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
return __ticket_spin_is_locked(lock);
@@ -129,8 +164,6 @@ static __always_inline void
arch_spin_lock_flags(arch_spinlock_t *lock,
arch_spin_lock(lock);
}
-#endif /* CONFIG_PARAVIRT_SPINLOCKS */
-
static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
while (arch_spin_is_locked(lock))
diff --git a/arch/x86/include/asm/spinlock_types.h
b/arch/x86/include/asm/spinlock_types.h
index ad0ad07..83fd3c7 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -1,10 +1,6 @@
#ifndef _ASM_X86_SPINLOCK_TYPES_H
#define _ASM_X86_SPINLOCK_TYPES_H
-#ifndef __LINUX_SPINLOCK_TYPES_H
-# error "please don't include this file directly"
-#endif
-
#include <linux/types.h>
#if (CONFIG_NR_CPUS < 256)
diff --git a/arch/x86/kernel/paravirt-spinlocks.c
b/arch/x86/kernel/paravirt-spinlocks.c
index 676b8c7..c2e010e 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -7,21 +7,10 @@
#include <asm/paravirt.h>
-static inline void
-default_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
-{
- arch_spin_lock(lock);
-}
-
struct pv_lock_ops pv_lock_ops = {
#ifdef CONFIG_SMP
- .spin_is_locked = __ticket_spin_is_locked,
- .spin_is_contended = __ticket_spin_is_contended,
-
- .spin_lock = __ticket_spin_lock,
- .spin_lock_flags = default_spin_lock_flags,
- .spin_trylock = __ticket_spin_trylock,
- .spin_unlock = __ticket_spin_unlock,
+ .lock_spinning = paravirt_nop,
+ .unlock_kick = paravirt_nop,
#endif
};
EXPORT_SYMBOL(pv_lock_ops);
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index cf3caee..d509629 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -139,6 +139,9 @@ struct xen_spinlock {
xen_spinners_t spinners; /* count of waiting cpus */
};
+static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
+
+#if 0
static int xen_spin_is_locked(struct arch_spinlock *lock)
{
struct xen_spinlock *xl = (struct xen_spinlock *)lock;
@@ -167,7 +170,6 @@ static int xen_spin_trylock(struct arch_spinlock *lock)
}
static DEFINE_PER_CPU(char *, irq_name);
-static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
/*
@@ -354,6 +356,7 @@ static void xen_spin_unlock(struct arch_spinlock *lock)
if (unlikely(xl->spinners))
xen_spin_unlock_slow(xl);
}
+#endif
static irqreturn_t dummy_handler(int irq, void *dev_id)
{
@@ -418,13 +421,14 @@ void __init xen_init_spinlocks(void)
return;
BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));
-
+#if 0
pv_lock_ops.spin_is_locked = xen_spin_is_locked;
pv_lock_ops.spin_is_contended = xen_spin_is_contended;
pv_lock_ops.spin_lock = xen_spin_lock;
pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
pv_lock_ops.spin_trylock = xen_spin_trylock;
pv_lock_ops.spin_unlock = xen_spin_unlock;
+#endif
}
#ifdef CONFIG_XEN_DEBUG_FS
Raghavendra K T
2013-Aug-06 11:41 UTC
[PATCH V12 2/14] x86/ticketlock: Don't inline _spin_unlock when using paravirt spinlocks
x86/ticketlock: Don't inline _spin_unlock when using paravirt spinlocks From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> The code size expands somewhat, and its better to just call a function rather than inline it. Thanks Jeremy for original version of ARCH_NOINLINE_SPIN_UNLOCK config patch, which is simplified. Suggested-by: Linus Torvalds <torvalds at linux-foundation.org> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com> Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> Acked-by: Ingo Molnar <mingo at kernel.org> --- arch/x86/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 7f3867c..724ce55 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -663,6 +663,7 @@ config PARAVIRT_DEBUG config PARAVIRT_SPINLOCKS bool "Paravirtualization layer for spinlocks" depends on PARAVIRT && SMP + select UNINLINE_SPIN_UNLOCK ---help--- Paravirtualized spinlocks allow a pvops backend to replace the spinlock implementation with something virtualization-friendly
Raghavendra K T
2013-Aug-06 11:41 UTC
[PATCH V12 3/14] x86/ticketlock: Collapse a layer of functions
x86/ticketlock: Collapse a layer of functions
From: Jeremy Fitzhardinge <jeremy at goop.org>
Now that the paravirtualization layer doesn't exist at the spinlock
level any more, we can collapse the __ticket_ functions into the arch_
functions.
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Tested-by: Attilio Rao <attilio.rao at citrix.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/include/asm/spinlock.h | 35 +++++------------------------------
1 file changed, 5 insertions(+), 30 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 4d54244..7442410 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -76,7 +76,7 @@ static __always_inline void __ticket_unlock_kick(struct
arch_spinlock *lock,
* in the high part, because a wide xadd increment of the low part would carry
* up and contaminate the high part.
*/
-static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
+static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
{
register struct __raw_tickets inc = { .tail = 1 };
@@ -96,7 +96,7 @@ static __always_inline void __ticket_spin_lock(struct
arch_spinlock *lock)
out: barrier(); /* make sure nothing creeps before the lock is taken */
}
-static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
+static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
{
arch_spinlock_t old, new;
@@ -110,7 +110,7 @@ static __always_inline int
__ticket_spin_trylock(arch_spinlock_t *lock)
return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) ==
old.head_tail;
}
-static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
+static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
{
__ticket_t next = lock->tickets.head + 1;
@@ -118,46 +118,21 @@ static __always_inline void
__ticket_spin_unlock(arch_spinlock_t *lock)
__ticket_unlock_kick(lock, next);
}
-static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
+static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
return tmp.tail != tmp.head;
}
-static inline int __ticket_spin_is_contended(arch_spinlock_t *lock)
+static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
return (__ticket_t)(tmp.tail - tmp.head) > 1;
}
-
-static inline int arch_spin_is_locked(arch_spinlock_t *lock)
-{
- return __ticket_spin_is_locked(lock);
-}
-
-static inline int arch_spin_is_contended(arch_spinlock_t *lock)
-{
- return __ticket_spin_is_contended(lock);
-}
#define arch_spin_is_contended arch_spin_is_contended
-static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
-{
- __ticket_spin_lock(lock);
-}
-
-static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
-{
- return __ticket_spin_trylock(lock);
-}
-
-static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
- __ticket_spin_unlock(lock);
-}
-
static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
unsigned long flags)
{
Raghavendra K T
2013-Aug-06 11:41 UTC
[PATCH V12 4/14] xen: Defer spinlock setup until boot CPU setup
xen: Defer spinlock setup until boot CPU setup
From: Jeremy Fitzhardinge <jeremy at goop.org>
There's no need to do it at very early init, and doing it there
makes it impossible to use the jump_label machinery.
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/xen/smp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index ca92754..3b52d80 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -279,6 +279,7 @@ static void __init xen_smp_prepare_boot_cpu(void)
xen_filter_cpu_maps();
xen_setup_vcpu_info_placement();
+ xen_init_spinlocks();
}
static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
@@ -680,7 +681,6 @@ void __init xen_smp_init(void)
{
smp_ops = xen_smp_ops;
xen_fill_possible_map();
- xen_init_spinlocks();
}
static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
Raghavendra K T
2013-Aug-06 11:42 UTC
[PATCH V12 5/14] xen/pvticketlock: Xen implementation for PV ticket locks
xen/pvticketlock: Xen implementation for PV ticket locks
From: Jeremy Fitzhardinge <jeremy at goop.org>
Replace the old Xen implementation of PV spinlocks with and implementation
of xen_lock_spinning and xen_unlock_kick.
xen_lock_spinning simply registers the cpu in its entry in lock_waiting,
adds itself to the waiting_cpus set, and blocks on an event channel
until the channel becomes pending.
xen_unlock_kick searches the cpus in waiting_cpus looking for the one
which next wants this lock with the next ticket, if any. If found,
it kicks it by making its event channel pending, which wakes it up.
We need to make sure interrupts are disabled while we're relying on the
contents of the per-cpu lock_waiting values, otherwise an interrupt
handler could come in, try to take some other lock, block, and overwrite
our values.
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
[ Raghavendra: use function + enum instead of macro, cmpxchg for zero status
reset
Reintroduce break since we know the exact vCPU to send IPI as suggested by
Konrad.]
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/xen/spinlock.c | 348 +++++++++++------------------------------------
1 file changed, 79 insertions(+), 269 deletions(-)
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index d509629..a458729 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -17,45 +17,44 @@
#include "xen-ops.h"
#include "debugfs.h"
-#ifdef CONFIG_XEN_DEBUG_FS
-static struct xen_spinlock_stats
-{
- u64 taken;
- u32 taken_slow;
- u32 taken_slow_nested;
- u32 taken_slow_pickup;
- u32 taken_slow_spurious;
- u32 taken_slow_irqenable;
+enum xen_contention_stat {
+ TAKEN_SLOW,
+ TAKEN_SLOW_PICKUP,
+ TAKEN_SLOW_SPURIOUS,
+ RELEASED_SLOW,
+ RELEASED_SLOW_KICKED,
+ NR_CONTENTION_STATS
+};
- u64 released;
- u32 released_slow;
- u32 released_slow_kicked;
+#ifdef CONFIG_XEN_DEBUG_FS
#define HISTO_BUCKETS 30
- u32 histo_spin_total[HISTO_BUCKETS+1];
- u32 histo_spin_spinning[HISTO_BUCKETS+1];
+static struct xen_spinlock_stats
+{
+ u32 contention_stats[NR_CONTENTION_STATS];
u32 histo_spin_blocked[HISTO_BUCKETS+1];
-
- u64 time_total;
- u64 time_spinning;
u64 time_blocked;
} spinlock_stats;
static u8 zero_stats;
-static unsigned lock_timeout = 1 << 10;
-#define TIMEOUT lock_timeout
-
static inline void check_zero(void)
{
- if (unlikely(zero_stats)) {
- memset(&spinlock_stats, 0, sizeof(spinlock_stats));
- zero_stats = 0;
+ u8 ret;
+ u8 old = ACCESS_ONCE(zero_stats);
+ if (unlikely(old)) {
+ ret = cmpxchg(&zero_stats, old, 0);
+ /* This ensures only one fellow resets the stat */
+ if (ret == old)
+ memset(&spinlock_stats, 0, sizeof(spinlock_stats));
}
}
-#define ADD_STATS(elem, val) \
- do { check_zero(); spinlock_stats.elem += (val); } while(0)
+static inline void add_stats(enum xen_contention_stat var, u32 val)
+{
+ check_zero();
+ spinlock_stats.contention_stats[var] += val;
+}
static inline u64 spin_time_start(void)
{
@@ -74,22 +73,6 @@ static void __spin_time_accum(u64 delta, u32 *array)
array[HISTO_BUCKETS]++;
}
-static inline void spin_time_accum_spinning(u64 start)
-{
- u32 delta = xen_clocksource_read() - start;
-
- __spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
- spinlock_stats.time_spinning += delta;
-}
-
-static inline void spin_time_accum_total(u64 start)
-{
- u32 delta = xen_clocksource_read() - start;
-
- __spin_time_accum(delta, spinlock_stats.histo_spin_total);
- spinlock_stats.time_total += delta;
-}
-
static inline void spin_time_accum_blocked(u64 start)
{
u32 delta = xen_clocksource_read() - start;
@@ -99,19 +82,15 @@ static inline void spin_time_accum_blocked(u64 start)
}
#else /* !CONFIG_XEN_DEBUG_FS */
#define TIMEOUT (1 << 10)
-#define ADD_STATS(elem, val) do { (void)(val); } while(0)
+static inline void add_stats(enum xen_contention_stat var, u32 val)
+{
+}
static inline u64 spin_time_start(void)
{
return 0;
}
-static inline void spin_time_accum_total(u64 start)
-{
-}
-static inline void spin_time_accum_spinning(u64 start)
-{
-}
static inline void spin_time_accum_blocked(u64 start)
{
}
@@ -134,230 +113,84 @@ typedef u16 xen_spinners_t;
asm(LOCK_PREFIX " decw %0" : "+m" ((xl)->spinners) : :
"memory");
#endif
-struct xen_spinlock {
- unsigned char lock; /* 0 -> free; 1 -> locked */
- xen_spinners_t spinners; /* count of waiting cpus */
+struct xen_lock_waiting {
+ struct arch_spinlock *lock;
+ __ticket_t want;
};
static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
-
-#if 0
-static int xen_spin_is_locked(struct arch_spinlock *lock)
-{
- struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-
- return xl->lock != 0;
-}
-
-static int xen_spin_is_contended(struct arch_spinlock *lock)
-{
- struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-
- /* Not strictly true; this is only the count of contended
- lock-takers entering the slow path. */
- return xl->spinners != 0;
-}
-
-static int xen_spin_trylock(struct arch_spinlock *lock)
-{
- struct xen_spinlock *xl = (struct xen_spinlock *)lock;
- u8 old = 1;
-
- asm("xchgb %b0,%1"
- : "+q" (old), "+m" (xl->lock) : :
"memory");
-
- return old == 0;
-}
-
static DEFINE_PER_CPU(char *, irq_name);
-static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
+static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
+static cpumask_t waiting_cpus;
-/*
- * Mark a cpu as interested in a lock. Returns the CPU's previous
- * lock of interest, in case we got preempted by an interrupt.
- */
-static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
+static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
{
- struct xen_spinlock *prev;
-
- prev = __this_cpu_read(lock_spinners);
- __this_cpu_write(lock_spinners, xl);
-
- wmb(); /* set lock of interest before count */
-
- inc_spinners(xl);
-
- return prev;
-}
-
-/*
- * Mark a cpu as no longer interested in a lock. Restores previous
- * lock of interest (NULL for none).
- */
-static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock
*prev)
-{
- dec_spinners(xl);
- wmb(); /* decrement count before restoring lock */
- __this_cpu_write(lock_spinners, prev);
-}
-
-static noinline int xen_spin_lock_slow(struct arch_spinlock *lock, bool
irq_enable)
-{
- struct xen_spinlock *xl = (struct xen_spinlock *)lock;
- struct xen_spinlock *prev;
int irq = __this_cpu_read(lock_kicker_irq);
- int ret;
+ struct xen_lock_waiting *w = &__get_cpu_var(lock_waiting);
+ int cpu = smp_processor_id();
u64 start;
+ unsigned long flags;
/* If kicker interrupts not initialized yet, just spin */
if (irq == -1)
- return 0;
+ return;
start = spin_time_start();
- /* announce we're spinning */
- prev = spinning_lock(xl);
-
- ADD_STATS(taken_slow, 1);
- ADD_STATS(taken_slow_nested, prev != NULL);
-
- do {
- unsigned long flags;
-
- /* clear pending */
- xen_clear_irq_pending(irq);
-
- /* check again make sure it didn't become free while
- we weren't looking */
- ret = xen_spin_trylock(lock);
- if (ret) {
- ADD_STATS(taken_slow_pickup, 1);
-
- /*
- * If we interrupted another spinlock while it
- * was blocking, make sure it doesn't block
- * without rechecking the lock.
- */
- if (prev != NULL)
- xen_set_irq_pending(irq);
- goto out;
- }
+ /*
+ * Make sure an interrupt handler can't upset things in a
+ * partially setup state.
+ */
+ local_irq_save(flags);
- flags = arch_local_save_flags();
- if (irq_enable) {
- ADD_STATS(taken_slow_irqenable, 1);
- raw_local_irq_enable();
- }
+ w->want = want;
+ smp_wmb();
+ w->lock = lock;
- /*
- * Block until irq becomes pending. If we're
- * interrupted at this point (after the trylock but
- * before entering the block), then the nested lock
- * handler guarantees that the irq will be left
- * pending if there's any chance the lock became free;
- * xen_poll_irq() returns immediately if the irq is
- * pending.
- */
- xen_poll_irq(irq);
+ /* This uses set_bit, which atomic and therefore a barrier */
+ cpumask_set_cpu(cpu, &waiting_cpus);
+ add_stats(TAKEN_SLOW, 1);
- raw_local_irq_restore(flags);
+ /* clear pending */
+ xen_clear_irq_pending(irq);
- ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
- } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
+ /* Only check lock once pending cleared */
+ barrier();
+ /* check again make sure it didn't become free while
+ we weren't looking */
+ if (ACCESS_ONCE(lock->tickets.head) == want) {
+ add_stats(TAKEN_SLOW_PICKUP, 1);
+ goto out;
+ }
+ /* Block until irq becomes pending (or perhaps a spurious wakeup) */
+ xen_poll_irq(irq);
+ add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
-
out:
- unspinning_lock(xl, prev);
+ cpumask_clear_cpu(cpu, &waiting_cpus);
+ w->lock = NULL;
+ local_irq_restore(flags);
spin_time_accum_blocked(start);
-
- return ret;
}
-static inline void __xen_spin_lock(struct arch_spinlock *lock, bool irq_enable)
-{
- struct xen_spinlock *xl = (struct xen_spinlock *)lock;
- unsigned timeout;
- u8 oldval;
- u64 start_spin;
-
- ADD_STATS(taken, 1);
-
- start_spin = spin_time_start();
-
- do {
- u64 start_spin_fast = spin_time_start();
-
- timeout = TIMEOUT;
-
- asm("1: xchgb %1,%0\n"
- " testb %1,%1\n"
- " jz 3f\n"
- "2: rep;nop\n"
- " cmpb $0,%0\n"
- " je 1b\n"
- " dec %2\n"
- " jnz 2b\n"
- "3:\n"
- : "+m" (xl->lock), "=q" (oldval), "+r"
(timeout)
- : "1" (1)
- : "memory");
-
- spin_time_accum_spinning(start_spin_fast);
-
- } while (unlikely(oldval != 0 &&
- (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));
-
- spin_time_accum_total(start_spin);
-}
-
-static void xen_spin_lock(struct arch_spinlock *lock)
-{
- __xen_spin_lock(lock, false);
-}
-
-static void xen_spin_lock_flags(struct arch_spinlock *lock, unsigned long
flags)
-{
- __xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
-}
-
-static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
+static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
{
int cpu;
- ADD_STATS(released_slow, 1);
+ add_stats(RELEASED_SLOW, 1);
+
+ for_each_cpu(cpu, &waiting_cpus) {
+ const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
- for_each_online_cpu(cpu) {
- /* XXX should mix up next cpu selection */
- if (per_cpu(lock_spinners, cpu) == xl) {
- ADD_STATS(released_slow_kicked, 1);
+ if (w->lock == lock && w->want == next) {
+ add_stats(RELEASED_SLOW_KICKED, 1);
xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
+ break;
}
}
}
-static void xen_spin_unlock(struct arch_spinlock *lock)
-{
- struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-
- ADD_STATS(released, 1);
-
- smp_wmb(); /* make sure no writes get moved after unlock */
- xl->lock = 0; /* release lock */
-
- /*
- * Make sure unlock happens before checking for waiting
- * spinners. We need a strong barrier to enforce the
- * write-read ordering to different memory locations, as the
- * CPU makes no implied guarantees about their ordering.
- */
- mb();
-
- if (unlikely(xl->spinners))
- xen_spin_unlock_slow(xl);
-}
-#endif
-
static irqreturn_t dummy_handler(int irq, void *dev_id)
{
BUG();
@@ -420,15 +253,8 @@ void __init xen_init_spinlocks(void)
if (xen_hvm_domain())
return;
- BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));
-#if 0
- pv_lock_ops.spin_is_locked = xen_spin_is_locked;
- pv_lock_ops.spin_is_contended = xen_spin_is_contended;
- pv_lock_ops.spin_lock = xen_spin_lock;
- pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
- pv_lock_ops.spin_trylock = xen_spin_trylock;
- pv_lock_ops.spin_unlock = xen_spin_unlock;
-#endif
+ pv_lock_ops.lock_spinning = xen_lock_spinning;
+ pv_lock_ops.unlock_kick = xen_unlock_kick;
}
#ifdef CONFIG_XEN_DEBUG_FS
@@ -446,37 +272,21 @@ static int __init xen_spinlock_debugfs(void)
debugfs_create_u8("zero_stats", 0644, d_spin_debug,
&zero_stats);
- debugfs_create_u32("timeout", 0644, d_spin_debug,
&lock_timeout);
-
- debugfs_create_u64("taken", 0444, d_spin_debug,
&spinlock_stats.taken);
debugfs_create_u32("taken_slow", 0444, d_spin_debug,
- &spinlock_stats.taken_slow);
- debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
- &spinlock_stats.taken_slow_nested);
+ &spinlock_stats.contention_stats[TAKEN_SLOW]);
debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
- &spinlock_stats.taken_slow_pickup);
+ &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
- &spinlock_stats.taken_slow_spurious);
- debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
- &spinlock_stats.taken_slow_irqenable);
+ &spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
- debugfs_create_u64("released", 0444, d_spin_debug,
&spinlock_stats.released);
debugfs_create_u32("released_slow", 0444, d_spin_debug,
- &spinlock_stats.released_slow);
+ &spinlock_stats.contention_stats[RELEASED_SLOW]);
debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
- &spinlock_stats.released_slow_kicked);
+ &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
- debugfs_create_u64("time_spinning", 0444, d_spin_debug,
- &spinlock_stats.time_spinning);
debugfs_create_u64("time_blocked", 0444, d_spin_debug,
&spinlock_stats.time_blocked);
- debugfs_create_u64("time_total", 0444, d_spin_debug,
- &spinlock_stats.time_total);
- debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
- spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
- debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
- spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
Raghavendra K T
2013-Aug-06 11:42 UTC
[PATCH V12 6/14] xen/pvticketlocks: Add xen_nopvspin parameter to disable xen pv ticketlocks
xen/pvticketlocks: Add xen_nopvspin parameter to disable xen pv ticketlocks
From: Jeremy Fitzhardinge <jeremy at goop.org>
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/xen/spinlock.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index a458729..669a971 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -244,6 +244,8 @@ void xen_uninit_lock_cpu(int cpu)
per_cpu(irq_name, cpu) = NULL;
}
+static bool xen_pvspin __initdata = true;
+
void __init xen_init_spinlocks(void)
{
/*
@@ -253,10 +255,22 @@ void __init xen_init_spinlocks(void)
if (xen_hvm_domain())
return;
+ if (!xen_pvspin) {
+ printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
+ return;
+ }
+
pv_lock_ops.lock_spinning = xen_lock_spinning;
pv_lock_ops.unlock_kick = xen_unlock_kick;
}
+static __init int xen_parse_nopvspin(char *arg)
+{
+ xen_pvspin = false;
+ return 0;
+}
+early_param("xen_nopvspin", xen_parse_nopvspin);
+
#ifdef CONFIG_XEN_DEBUG_FS
static struct dentry *d_spin_debug;
Raghavendra K T
2013-Aug-06 11:42 UTC
[PATCH V12 7/14] x86/pvticketlock: Use callee-save for lock_spinning
x86/pvticketlock: Use callee-save for lock_spinning
From: Jeremy Fitzhardinge <jeremy at goop.org>
Although the lock_spinning calls in the spinlock code are on the
uncommon path, their presence can cause the compiler to generate many
more register save/restores in the function pre/postamble, which is in
the fast path. To avoid this, convert it to using the pvops callee-save
calling convention, which defers all the save/restores until the actual
function is called, keeping the fastpath clean.
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Tested-by: Attilio Rao <attilio.rao at citrix.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/include/asm/paravirt.h | 2 +-
arch/x86/include/asm/paravirt_types.h | 2 +-
arch/x86/kernel/paravirt-spinlocks.c | 2 +-
arch/x86/xen/spinlock.c | 3 ++-
4 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 040e72d..7131e12c 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -715,7 +715,7 @@ static inline void __set_fixmap(unsigned /* enum
fixed_addresses */ idx,
static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
__ticket_t ticket)
{
- PVOP_VCALL2(pv_lock_ops.lock_spinning, lock, ticket);
+ PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
}
static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index d5deb6d..350d017 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -330,7 +330,7 @@ struct arch_spinlock;
#include <asm/spinlock_types.h>
struct pv_lock_ops {
- void (*lock_spinning)(struct arch_spinlock *lock, __ticket_t ticket);
+ struct paravirt_callee_save lock_spinning;
void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
};
diff --git a/arch/x86/kernel/paravirt-spinlocks.c
b/arch/x86/kernel/paravirt-spinlocks.c
index c2e010e..4251c1d 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -9,7 +9,7 @@
struct pv_lock_ops pv_lock_ops = {
#ifdef CONFIG_SMP
- .lock_spinning = paravirt_nop,
+ .lock_spinning = __PV_IS_CALLEE_SAVE(paravirt_nop),
.unlock_kick = paravirt_nop,
#endif
};
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 669a971..6c8792b 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -173,6 +173,7 @@ out:
local_irq_restore(flags);
spin_time_accum_blocked(start);
}
+PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
{
@@ -260,7 +261,7 @@ void __init xen_init_spinlocks(void)
return;
}
- pv_lock_ops.lock_spinning = xen_lock_spinning;
+ pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
pv_lock_ops.unlock_kick = xen_unlock_kick;
}
Raghavendra K T
2013-Aug-06 11:43 UTC
[PATCH V12 8/14] x86/pvticketlock: When paravirtualizing ticket locks, increment by 2
x86/pvticketlock: When paravirtualizing ticket locks, increment by 2
From: Jeremy Fitzhardinge <jeremy at goop.org>
Increment ticket head/tails by 2 rather than 1 to leave the LSB free
to store a "is in slowpath state" bit. This halves the number
of possible CPUs for a given ticket size, but this shouldn't matter
in practice - kernels built for 32k+ CPU systems are probably
specially built for the hardware rather than a generic distro
kernel.
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Tested-by: Attilio Rao <attilio.rao at citrix.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/include/asm/spinlock.h | 10 +++++-----
arch/x86/include/asm/spinlock_types.h | 10 +++++++++-
2 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 7442410..04a5cd5 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -78,7 +78,7 @@ static __always_inline void __ticket_unlock_kick(struct
arch_spinlock *lock,
*/
static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
{
- register struct __raw_tickets inc = { .tail = 1 };
+ register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
inc = xadd(&lock->tickets, inc);
@@ -104,7 +104,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t
*lock)
if (old.tickets.head != old.tickets.tail)
return 0;
- new.head_tail = old.head_tail + (1 << TICKET_SHIFT);
+ new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
/* cmpxchg is a full barrier, so nothing can move before it */
return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) ==
old.head_tail;
@@ -112,9 +112,9 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t
*lock)
static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
{
- __ticket_t next = lock->tickets.head + 1;
+ __ticket_t next = lock->tickets.head + TICKET_LOCK_INC;
- __add(&lock->tickets.head, 1, UNLOCK_LOCK_PREFIX);
+ __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
__ticket_unlock_kick(lock, next);
}
@@ -129,7 +129,7 @@ static inline int arch_spin_is_contended(arch_spinlock_t
*lock)
{
struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
- return (__ticket_t)(tmp.tail - tmp.head) > 1;
+ return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
}
#define arch_spin_is_contended arch_spin_is_contended
diff --git a/arch/x86/include/asm/spinlock_types.h
b/arch/x86/include/asm/spinlock_types.h
index 83fd3c7..e96fcbd 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -3,7 +3,13 @@
#include <linux/types.h>
-#if (CONFIG_NR_CPUS < 256)
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#define __TICKET_LOCK_INC 2
+#else
+#define __TICKET_LOCK_INC 1
+#endif
+
+#if (CONFIG_NR_CPUS < (256 / __TICKET_LOCK_INC))
typedef u8 __ticket_t;
typedef u16 __ticketpair_t;
#else
@@ -11,6 +17,8 @@ typedef u16 __ticket_t;
typedef u32 __ticketpair_t;
#endif
+#define TICKET_LOCK_INC ((__ticket_t)__TICKET_LOCK_INC)
+
#define TICKET_SHIFT (sizeof(__ticket_t) * 8)
typedef struct arch_spinlock {
Raghavendra K T
2013-Aug-06 11:43 UTC
[PATCH V12 9/14] jump_label: Split out rate limiting from jump_label.h
jump_label: Split jumplabel ratelimit
From: Andrew Jones <drjones at redhat.com>
Commit b202952075f62603bea9bfb6ebc6b0420db11949 ("perf, core: Rate limit
perf_sched_events jump_label patching") introduced rate limiting
for jump label disabling. The changes were made in the jump label code
in order to be more widely available and to keep things tidier. This is
all fine, except now jump_label.h includes linux/workqueue.h, which
makes it impossible to include jump_label.h from anything that
workqueue.h needs. For example, it's now impossible to include
jump_label.h from asm/spinlock.h, which is done in proposed
pv-ticketlock patches. This patch splits out the rate limiting related
changes from jump_label.h into a new file, jump_label_ratelimit.h, to
resolve the issue.
Signed-off-by: Andrew Jones <drjones at redhat.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
include/linux/jump_label.h | 26 +-------------------------
include/linux/jump_label_ratelimit.h | 34 ++++++++++++++++++++++++++++++++++
include/linux/perf_event.h | 1 +
kernel/jump_label.c | 1 +
4 files changed, 37 insertions(+), 25 deletions(-)
create mode 100644 include/linux/jump_label_ratelimit.h
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 0976fc4..53cdf89 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -48,7 +48,6 @@
#include <linux/types.h>
#include <linux/compiler.h>
-#include <linux/workqueue.h>
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
@@ -61,12 +60,6 @@ struct static_key {
#endif
};
-struct static_key_deferred {
- struct static_key key;
- unsigned long timeout;
- struct delayed_work work;
-};
-
# include <asm/jump_label.h>
# define HAVE_JUMP_LABEL
#endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */
@@ -119,10 +112,7 @@ extern void arch_jump_label_transform_static(struct
jump_entry *entry,
extern int jump_label_text_reserved(void *start, void *end);
extern void static_key_slow_inc(struct static_key *key);
extern void static_key_slow_dec(struct static_key *key);
-extern void static_key_slow_dec_deferred(struct static_key_deferred *key);
extern void jump_label_apply_nops(struct module *mod);
-extern void
-jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl);
#define STATIC_KEY_INIT_TRUE ((struct static_key) \
{ .enabled = ATOMIC_INIT(1), .entries = (void *)1 })
@@ -141,10 +131,6 @@ static __always_inline void jump_label_init(void)
{
}
-struct static_key_deferred {
- struct static_key key;
-};
-
static __always_inline bool static_key_false(struct static_key *key)
{
if (unlikely(atomic_read(&key->enabled)) > 0)
@@ -169,11 +155,6 @@ static inline void static_key_slow_dec(struct static_key
*key)
atomic_dec(&key->enabled);
}
-static inline void static_key_slow_dec_deferred(struct static_key_deferred
*key)
-{
- static_key_slow_dec(&key->key);
-}
-
static inline int jump_label_text_reserved(void *start, void *end)
{
return 0;
@@ -187,12 +168,6 @@ static inline int jump_label_apply_nops(struct module *mod)
return 0;
}
-static inline void
-jump_label_rate_limit(struct static_key_deferred *key,
- unsigned long rl)
-{
-}
-
#define STATIC_KEY_INIT_TRUE ((struct static_key) \
{ .enabled = ATOMIC_INIT(1) })
#define STATIC_KEY_INIT_FALSE ((struct static_key) \
@@ -203,6 +178,7 @@ jump_label_rate_limit(struct static_key_deferred *key,
#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
#define jump_label_enabled static_key_enabled
+static inline int atomic_read(const atomic_t *v);
static inline bool static_key_enabled(struct static_key *key)
{
return (atomic_read(&key->enabled) > 0);
diff --git a/include/linux/jump_label_ratelimit.h
b/include/linux/jump_label_ratelimit.h
new file mode 100644
index 0000000..1137883
--- /dev/null
+++ b/include/linux/jump_label_ratelimit.h
@@ -0,0 +1,34 @@
+#ifndef _LINUX_JUMP_LABEL_RATELIMIT_H
+#define _LINUX_JUMP_LABEL_RATELIMIT_H
+
+#include <linux/jump_label.h>
+#include <linux/workqueue.h>
+
+#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
+struct static_key_deferred {
+ struct static_key key;
+ unsigned long timeout;
+ struct delayed_work work;
+};
+#endif
+
+#ifdef HAVE_JUMP_LABEL
+extern void static_key_slow_dec_deferred(struct static_key_deferred *key);
+extern void
+jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl);
+
+#else /* !HAVE_JUMP_LABEL */
+struct static_key_deferred {
+ struct static_key key;
+};
+static inline void static_key_slow_dec_deferred(struct static_key_deferred
*key)
+{
+ static_key_slow_dec(&key->key);
+}
+static inline void
+jump_label_rate_limit(struct static_key_deferred *key,
+ unsigned long rl)
+{
+}
+#endif /* HAVE_JUMP_LABEL */
+#endif /* _LINUX_JUMP_LABEL_RATELIMIT_H */
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c43f6ea..226be8d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -48,6 +48,7 @@ struct perf_guest_info_callbacks {
#include <linux/cpu.h>
#include <linux/irq_work.h>
#include <linux/static_key.h>
+#include <linux/jump_label_ratelimit.h>
#include <linux/atomic.h>
#include <linux/sysfs.h>
#include <linux/perf_regs.h>
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 60f48fa..297a924 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -13,6 +13,7 @@
#include <linux/sort.h>
#include <linux/err.h>
#include <linux/static_key.h>
+#include <linux/jump_label_ratelimit.h>
#ifdef HAVE_JUMP_LABEL
Raghavendra K T
2013-Aug-06 11:43 UTC
[PATCH V12 10/14] x86/ticketlock: Add slowpath logic
x86/ticketlock: Add slowpath logic
From: Jeremy Fitzhardinge <jeremy at goop.org>
Maintain a flag in the LSB of the ticket lock tail which indicates
whether anyone is in the lock slowpath and may need kicking when
the current holder unlocks. The flags are set when the first locker
enters the slowpath, and cleared when unlocking to an empty queue (ie,
no contention).
In the specific implementation of lock_spinning(), make sure to set
the slowpath flags on the lock just before blocking. We must do
this before the last-chance pickup test to prevent a deadlock
with the unlocker:
Unlocker Locker
test for lock pickup
-> fail
unlock
test slowpath
-> false
set slowpath flags
block
Whereas this works in any ordering:
Unlocker Locker
set slowpath flags
test for lock pickup
-> fail
block
unlock
test slowpath
-> true, kick
If the unlocker finds that the lock has the slowpath flag set but it is
actually uncontended (ie, head == tail, so nobody is waiting), then it
clears the slowpath flag.
The unlock code uses a locked add to update the head counter. This also
acts as a full memory barrier so that its safe to subsequently
read back the slowflag state, knowing that the updated lock is visible
to the other CPUs. If it were an unlocked add, then the flag read may
just be forwarded from the store buffer before it was visible to the other
CPUs, which could result in a deadlock.
Unfortunately this means we need to do a locked instruction when
unlocking with PV ticketlocks. However, if PV ticketlocks are not
enabled, then the old non-locked "add" is the only unlocking code.
Note: this code relies on gcc making sure that unlikely() code is out of
line of the fastpath, which only happens when OPTIMIZE_SIZE=n. If it
doesn't the generated code isn't too bad, but its definitely suboptimal.
Thanks to Srivatsa Vaddagiri for providing a bugfix to the original
version of this change, which has been folded in.
Thanks to Stephan Diestelhorst for commenting on some code which relied
on an inaccurate reading of the x86 memory ordering rules.
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Signed-off-by: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Cc: Stephan Diestelhorst <stephan.diestelhorst at amd.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/include/asm/paravirt.h | 2 -
arch/x86/include/asm/spinlock.h | 86 ++++++++++++++++++++++++---------
arch/x86/include/asm/spinlock_types.h | 2 +
arch/x86/kernel/paravirt-spinlocks.c | 3 +
arch/x86/xen/spinlock.c | 6 ++
5 files changed, 74 insertions(+), 25 deletions(-)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 7131e12c..401f350 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -718,7 +718,7 @@ static __always_inline void __ticket_lock_spinning(struct
arch_spinlock *lock,
PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
}
-static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
+static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
__ticket_t ticket)
{
PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 04a5cd5..d68883d 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -1,11 +1,14 @@
#ifndef _ASM_X86_SPINLOCK_H
#define _ASM_X86_SPINLOCK_H
+#include <linux/jump_label.h>
#include <linux/atomic.h>
#include <asm/page.h>
#include <asm/processor.h>
#include <linux/compiler.h>
#include <asm/paravirt.h>
+#include <asm/bitops.h>
+
/*
* Your basic SMP spinlocks, allowing only a single CPU anywhere
*
@@ -37,32 +40,28 @@
/* How long a lock should spin before we consider blocking */
#define SPIN_THRESHOLD (1 << 15)
-#ifndef CONFIG_PARAVIRT_SPINLOCKS
+extern struct static_key paravirt_ticketlocks_enabled;
+static __always_inline bool static_key_false(struct static_key *key);
-static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
- __ticket_t ticket)
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
{
+ set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
}
-static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
- __ticket_t ticket)
+#else /* !CONFIG_PARAVIRT_SPINLOCKS */
+static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
+ __ticket_t ticket)
{
}
-
-#endif /* CONFIG_PARAVIRT_SPINLOCKS */
-
-
-/*
- * If a spinlock has someone waiting on it, then kick the appropriate
- * waiting cpu.
- */
-static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
- __ticket_t next)
+static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
+ __ticket_t ticket)
{
- if (unlikely(lock->tickets.tail != next))
- ____ticket_unlock_kick(lock, next);
}
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+
/*
* Ticket locks are conceptually two parts, one indicating the current head of
* the queue, and the other indicating the current tail. The lock is acquired
@@ -76,20 +75,22 @@ static __always_inline void __ticket_unlock_kick(struct
arch_spinlock *lock,
* in the high part, because a wide xadd increment of the low part would carry
* up and contaminate the high part.
*/
-static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
+static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
{
register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
inc = xadd(&lock->tickets, inc);
+ if (likely(inc.head == inc.tail))
+ goto out;
+ inc.tail &= ~TICKET_SLOWPATH_FLAG;
for (;;) {
unsigned count = SPIN_THRESHOLD;
do {
- if (inc.head == inc.tail)
+ if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
goto out;
cpu_relax();
- inc.head = ACCESS_ONCE(lock->tickets.head);
} while (--count);
__ticket_lock_spinning(lock, inc.tail);
}
@@ -101,7 +102,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t
*lock)
arch_spinlock_t old, new;
old.tickets = ACCESS_ONCE(lock->tickets);
- if (old.tickets.head != old.tickets.tail)
+ if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
return 0;
new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
@@ -110,12 +111,49 @@ static __always_inline int
arch_spin_trylock(arch_spinlock_t *lock)
return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) ==
old.head_tail;
}
+static inline void __ticket_unlock_slowpath(arch_spinlock_t *lock,
+ arch_spinlock_t old)
+{
+ arch_spinlock_t new;
+
+ BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
+
+ /* Perform the unlock on the "before" copy */
+ old.tickets.head += TICKET_LOCK_INC;
+
+ /* Clear the slowpath flag */
+ new.head_tail = old.head_tail & ~(TICKET_SLOWPATH_FLAG <<
TICKET_SHIFT);
+
+ /*
+ * If the lock is uncontended, clear the flag - use cmpxchg in
+ * case it changes behind our back though.
+ */
+ if (new.tickets.head != new.tickets.tail ||
+ cmpxchg(&lock->head_tail, old.head_tail,
+ new.head_tail) != old.head_tail) {
+ /*
+ * Lock still has someone queued for it, so wake up an
+ * appropriate waiter.
+ */
+ __ticket_unlock_kick(lock, old.tickets.head);
+ }
+}
+
static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
{
- __ticket_t next = lock->tickets.head + TICKET_LOCK_INC;
+ if (TICKET_SLOWPATH_FLAG &&
+ static_key_false(¶virt_ticketlocks_enabled)) {
+ arch_spinlock_t prev;
+
+ prev = *lock;
+ add_smp(&lock->tickets.head, TICKET_LOCK_INC);
+
+ /* add_smp() is a full mb() */
- __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
- __ticket_unlock_kick(lock, next);
+ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
+ __ticket_unlock_slowpath(lock, prev);
+ } else
+ __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
}
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
diff --git a/arch/x86/include/asm/spinlock_types.h
b/arch/x86/include/asm/spinlock_types.h
index e96fcbd..4f1bea1 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -5,8 +5,10 @@
#ifdef CONFIG_PARAVIRT_SPINLOCKS
#define __TICKET_LOCK_INC 2
+#define TICKET_SLOWPATH_FLAG ((__ticket_t)1)
#else
#define __TICKET_LOCK_INC 1
+#define TICKET_SLOWPATH_FLAG ((__ticket_t)0)
#endif
#if (CONFIG_NR_CPUS < (256 / __TICKET_LOCK_INC))
diff --git a/arch/x86/kernel/paravirt-spinlocks.c
b/arch/x86/kernel/paravirt-spinlocks.c
index 4251c1d..bbb6c73 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -4,6 +4,7 @@
*/
#include <linux/spinlock.h>
#include <linux/module.h>
+#include <linux/jump_label.h>
#include <asm/paravirt.h>
@@ -15,3 +16,5 @@ struct pv_lock_ops pv_lock_ops = {
};
EXPORT_SYMBOL(pv_lock_ops);
+struct static_key paravirt_ticketlocks_enabled = STATIC_KEY_INIT_FALSE;
+EXPORT_SYMBOL(paravirt_ticketlocks_enabled);
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 6c8792b..546112e 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -157,6 +157,10 @@ static void xen_lock_spinning(struct arch_spinlock *lock,
__ticket_t want)
/* Only check lock once pending cleared */
barrier();
+ /* Mark entry to slowpath before doing the pickup test to make
+ sure we don't deadlock with an unlocker. */
+ __ticket_enter_slowpath(lock);
+
/* check again make sure it didn't become free while
we weren't looking */
if (ACCESS_ONCE(lock->tickets.head) == want) {
@@ -261,6 +265,8 @@ void __init xen_init_spinlocks(void)
return;
}
+ static_key_slow_inc(¶virt_ticketlocks_enabled);
+
pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
pv_lock_ops.unlock_kick = xen_unlock_kick;
}
Raghavendra K T
2013-Aug-06 11:44 UTC
[PATCH V12 11/14] xen/pvticketlock: Allow interrupts to be enabled while blocking
xen/pvticketlock: Allow interrupts to be enabled while blocking
From: Jeremy Fitzhardinge <jeremy at goop.org>
If interrupts were enabled when taking the spinlock, we can leave them
enabled while blocking to get the lock.
If we can enable interrupts while waiting for the lock to become
available, and we take an interrupt before entering the poll,
and the handler takes a spinlock which ends up going into
the slow state (invalidating the per-cpu "lock" and "want"
values),
then when the interrupt handler returns the event channel will
remain pending so the poll will return immediately, causing it to
return out to the main spinlock loop.
Signed-off-by: Jeremy Fitzhardinge <jeremy at goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/xen/spinlock.c | 46 ++++++++++++++++++++++++++++++++++++++++------
1 file changed, 40 insertions(+), 6 deletions(-)
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 546112e..0438b93 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -142,7 +142,20 @@ static void xen_lock_spinning(struct arch_spinlock *lock,
__ticket_t want)
* partially setup state.
*/
local_irq_save(flags);
-
+ /*
+ * We don't really care if we're overwriting some other
+ * (lock,want) pair, as that would mean that we're currently
+ * in an interrupt context, and the outer context had
+ * interrupts enabled. That has already kicked the VCPU out
+ * of xen_poll_irq(), so it will just return spuriously and
+ * retry with newly setup (lock,want).
+ *
+ * The ordering protocol on this is that the "lock" pointer
+ * may only be set non-NULL if the "want" ticket is correct.
+ * If we're updating "want", we must first clear
"lock".
+ */
+ w->lock = NULL;
+ smp_wmb();
w->want = want;
smp_wmb();
w->lock = lock;
@@ -157,24 +170,43 @@ static void xen_lock_spinning(struct arch_spinlock *lock,
__ticket_t want)
/* Only check lock once pending cleared */
barrier();
- /* Mark entry to slowpath before doing the pickup test to make
- sure we don't deadlock with an unlocker. */
+ /*
+ * Mark entry to slowpath before doing the pickup test to make
+ * sure we don't deadlock with an unlocker.
+ */
__ticket_enter_slowpath(lock);
- /* check again make sure it didn't become free while
- we weren't looking */
+ /*
+ * check again make sure it didn't become free while
+ * we weren't looking
+ */
if (ACCESS_ONCE(lock->tickets.head) == want) {
add_stats(TAKEN_SLOW_PICKUP, 1);
goto out;
}
+
+ /* Allow interrupts while blocked */
+ local_irq_restore(flags);
+
+ /*
+ * If an interrupt happens here, it will leave the wakeup irq
+ * pending, which will cause xen_poll_irq() to return
+ * immediately.
+ */
+
/* Block until irq becomes pending (or perhaps a spurious wakeup) */
xen_poll_irq(irq);
add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
+
+ local_irq_save(flags);
+
kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
out:
cpumask_clear_cpu(cpu, &waiting_cpus);
w->lock = NULL;
+
local_irq_restore(flags);
+
spin_time_accum_blocked(start);
}
PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
@@ -188,7 +220,9 @@ static void xen_unlock_kick(struct arch_spinlock *lock,
__ticket_t next)
for_each_cpu(cpu, &waiting_cpus) {
const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
- if (w->lock == lock && w->want == next) {
+ /* Make sure we read lock before want */
+ if (ACCESS_ONCE(w->lock) == lock &&
+ ACCESS_ONCE(w->want) == next) {
add_stats(RELEASED_SLOW_KICKED, 1);
xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
break;
Raghavendra K T
2013-Aug-06 11:44 UTC
[PATCH V12 12/14] kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi
kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> this is needed by both guest and host. Originally-from: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com> Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> Acked-by: Gleb Natapov <gleb at redhat.com> Acked-by: Ingo Molnar <mingo at kernel.org> --- arch/x86/include/uapi/asm/kvm_para.h | 1 + include/uapi/linux/kvm_para.h | 1 + 2 files changed, 2 insertions(+) diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index 06fdbd9..94dc8ca 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -23,6 +23,7 @@ #define KVM_FEATURE_ASYNC_PF 4 #define KVM_FEATURE_STEAL_TIME 5 #define KVM_FEATURE_PV_EOI 6 +#define KVM_FEATURE_PV_UNHALT 7 /* The last 8 bits are used to indicate how to interpret the flags field * in pvclock structure. If no bits are set, all flags are ignored. diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h index cea2c5c..2841f86 100644 --- a/include/uapi/linux/kvm_para.h +++ b/include/uapi/linux/kvm_para.h @@ -19,6 +19,7 @@ #define KVM_HC_MMU_OP 2 #define KVM_HC_FEATURES 3 #define KVM_HC_PPC_MAP_MAGIC_PAGE 4 +#define KVM_HC_KICK_CPU 5 /* * hypercalls use architecture specific
Raghavendra K T
2013-Aug-06 11:45 UTC
[PATCH V12 13/14] kvm guest : Add configuration support to enable debug information for KVM Guests
kvm guest : Add configuration support to enable debug information for KVM Guests From: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com> Signed-off-by: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com> Signed-off-by: Suzuki Poulose <suzuki at in.ibm.com> Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com> Acked-by: Gleb Natapov <gleb at redhat.com> Acked-by: Ingo Molnar <mingo at kernel.org> --- arch/x86/Kconfig | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 724ce55..f108f00 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -688,6 +688,15 @@ config KVM_GUEST underlying device model, the host provides the guest with timing infrastructure such as time of day, and system time +config KVM_DEBUG_FS + bool "Enable debug information for KVM Guests in debugfs" + depends on KVM_GUEST && DEBUG_FS + default n + ---help--- + This option enables collection of various statistics for KVM guest. + Statistics are displayed in debugfs filesystem. Enabling this option + may incur significant overhead. + source "arch/x86/lguest/Kconfig" config PARAVIRT_TIME_ACCOUNTING
Raghavendra K T
2013-Aug-06 11:45 UTC
[PATCH V12 14/14] kvm : Paravirtual ticketlocks support for linux guests running on KVM hypervisor
kvm : Paravirtual ticketlocks support for linux guests running on KVM hypervisor
From: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com>
During smp_boot_cpus paravirtualied KVM guest detects if the hypervisor has
required feature (KVM_FEATURE_PV_UNHALT) to support pv-ticketlocks. If so,
support for pv-ticketlocks is registered via pv_lock_ops.
Use KVM_HC_KICK_CPU hypercall to wakeup waiting/halted vcpu.
Signed-off-by: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com>
Signed-off-by: Suzuki Poulose <suzuki at in.ibm.com>
[Raghu: check_zero race fix, enum for kvm_contention_stat, jumplabel related
changes,
addition of safe_halt for irq enabled case, bailout spinning in nmi case(Gleb)]
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb at redhat.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
arch/x86/include/asm/kvm_para.h | 14 ++
arch/x86/kernel/kvm.c | 262 +++++++++++++++++++++++++++++++++++++++
2 files changed, 274 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 695399f..427afcb 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -118,10 +118,20 @@ void kvm_async_pf_task_wait(u32 token);
void kvm_async_pf_task_wake(u32 token);
u32 kvm_read_and_reset_pf_reason(void);
extern void kvm_disable_steal_time(void);
-#else
-#define kvm_guest_init() do { } while (0)
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+void __init kvm_spinlock_init(void);
+#else /* !CONFIG_PARAVIRT_SPINLOCKS */
+static inline void kvm_spinlock_init(void)
+{
+}
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+
+#else /* CONFIG_KVM_GUEST */
+#define kvm_guest_init() do {} while (0)
#define kvm_async_pf_task_wait(T) do {} while(0)
#define kvm_async_pf_task_wake(T) do {} while(0)
+
static inline u32 kvm_read_and_reset_pf_reason(void)
{
return 0;
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index a96d32c..9b33a27 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -34,6 +34,7 @@
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/kprobes.h>
+#include <linux/debugfs.h>
#include <asm/timer.h>
#include <asm/cpu.h>
#include <asm/traps.h>
@@ -419,6 +420,7 @@ static void __init kvm_smp_prepare_boot_cpu(void)
WARN_ON(kvm_register_clock("primary cpu clock"));
kvm_guest_cpu_init();
native_smp_prepare_boot_cpu();
+ kvm_spinlock_init();
}
static void kvm_guest_cpu_online(void *dummy)
@@ -523,3 +525,263 @@ static __init int activate_jump_labels(void)
return 0;
}
arch_initcall(activate_jump_labels);
+
+/* Kick a cpu by its apicid. Used to wake up a halted vcpu */
+void kvm_kick_cpu(int cpu)
+{
+ int apicid;
+ unsigned long flags = 0;
+
+ apicid = per_cpu(x86_cpu_to_apicid, cpu);
+ kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
+}
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+enum kvm_contention_stat {
+ TAKEN_SLOW,
+ TAKEN_SLOW_PICKUP,
+ RELEASED_SLOW,
+ RELEASED_SLOW_KICKED,
+ NR_CONTENTION_STATS
+};
+
+#ifdef CONFIG_KVM_DEBUG_FS
+#define HISTO_BUCKETS 30
+
+static struct kvm_spinlock_stats
+{
+ u32 contention_stats[NR_CONTENTION_STATS];
+ u32 histo_spin_blocked[HISTO_BUCKETS+1];
+ u64 time_blocked;
+} spinlock_stats;
+
+static u8 zero_stats;
+
+static inline void check_zero(void)
+{
+ u8 ret;
+ u8 old;
+
+ old = ACCESS_ONCE(zero_stats);
+ if (unlikely(old)) {
+ ret = cmpxchg(&zero_stats, old, 0);
+ /* This ensures only one fellow resets the stat */
+ if (ret == old)
+ memset(&spinlock_stats, 0, sizeof(spinlock_stats));
+ }
+}
+
+static inline void add_stats(enum kvm_contention_stat var, u32 val)
+{
+ check_zero();
+ spinlock_stats.contention_stats[var] += val;
+}
+
+
+static inline u64 spin_time_start(void)
+{
+ return sched_clock();
+}
+
+static void __spin_time_accum(u64 delta, u32 *array)
+{
+ unsigned index;
+
+ index = ilog2(delta);
+ check_zero();
+
+ if (index < HISTO_BUCKETS)
+ array[index]++;
+ else
+ array[HISTO_BUCKETS]++;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+ u32 delta;
+
+ delta = sched_clock() - start;
+ __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
+ spinlock_stats.time_blocked += delta;
+}
+
+static struct dentry *d_spin_debug;
+static struct dentry *d_kvm_debug;
+
+struct dentry *kvm_init_debugfs(void)
+{
+ d_kvm_debug = debugfs_create_dir("kvm", NULL);
+ if (!d_kvm_debug)
+ printk(KERN_WARNING "Could not create 'kvm' debugfs
directory\n");
+
+ return d_kvm_debug;
+}
+
+static int __init kvm_spinlock_debugfs(void)
+{
+ struct dentry *d_kvm;
+
+ d_kvm = kvm_init_debugfs();
+ if (d_kvm == NULL)
+ return -ENOMEM;
+
+ d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
+
+ debugfs_create_u8("zero_stats", 0644, d_spin_debug,
&zero_stats);
+
+ debugfs_create_u32("taken_slow", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[TAKEN_SLOW]);
+ debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
+
+ debugfs_create_u32("released_slow", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[RELEASED_SLOW]);
+ debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
+
+ debugfs_create_u64("time_blocked", 0444, d_spin_debug,
+ &spinlock_stats.time_blocked);
+
+ debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
+ spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
+
+ return 0;
+}
+fs_initcall(kvm_spinlock_debugfs);
+#else /* !CONFIG_KVM_DEBUG_FS */
+static inline void add_stats(enum kvm_contention_stat var, u32 val)
+{
+}
+
+static inline u64 spin_time_start(void)
+{
+ return 0;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+}
+#endif /* CONFIG_KVM_DEBUG_FS */
+
+struct kvm_lock_waiting {
+ struct arch_spinlock *lock;
+ __ticket_t want;
+};
+
+/* cpus 'waiting' on a spinlock to become available */
+static cpumask_t waiting_cpus;
+
+/* Track spinlock on which a cpu is waiting */
+static DEFINE_PER_CPU(struct kvm_lock_waiting, lock_waiting);
+
+static void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
+{
+ struct kvm_lock_waiting *w;
+ int cpu;
+ u64 start;
+ unsigned long flags;
+
+ if (in_nmi())
+ return;
+
+ w = &__get_cpu_var(lock_waiting);
+ cpu = smp_processor_id();
+ start = spin_time_start();
+
+ /*
+ * Make sure an interrupt handler can't upset things in a
+ * partially setup state.
+ */
+ local_irq_save(flags);
+
+ /*
+ * The ordering protocol on this is that the "lock" pointer
+ * may only be set non-NULL if the "want" ticket is correct.
+ * If we're updating "want", we must first clear
"lock".
+ */
+ w->lock = NULL;
+ smp_wmb();
+ w->want = want;
+ smp_wmb();
+ w->lock = lock;
+
+ add_stats(TAKEN_SLOW, 1);
+
+ /*
+ * This uses set_bit, which is atomic but we should not rely on its
+ * reordering gurantees. So barrier is needed after this call.
+ */
+ cpumask_set_cpu(cpu, &waiting_cpus);
+
+ barrier();
+
+ /*
+ * Mark entry to slowpath before doing the pickup test to make
+ * sure we don't deadlock with an unlocker.
+ */
+ __ticket_enter_slowpath(lock);
+
+ /*
+ * check again make sure it didn't become free while
+ * we weren't looking.
+ */
+ if (ACCESS_ONCE(lock->tickets.head) == want) {
+ add_stats(TAKEN_SLOW_PICKUP, 1);
+ goto out;
+ }
+
+ /*
+ * halt until it's our turn and kicked. Note that we do safe halt
+ * for irq enabled case to avoid hang when lock info is overwritten
+ * in irq spinlock slowpath and no spurious interrupt occur to save us.
+ */
+ if (arch_irqs_disabled_flags(flags))
+ halt();
+ else
+ safe_halt();
+
+out:
+ cpumask_clear_cpu(cpu, &waiting_cpus);
+ w->lock = NULL;
+ local_irq_restore(flags);
+ spin_time_accum_blocked(start);
+}
+PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
+
+/* Kick vcpu waiting on @lock->head to reach value @ticket */
+static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
+{
+ int cpu;
+
+ add_stats(RELEASED_SLOW, 1);
+ for_each_cpu(cpu, &waiting_cpus) {
+ const struct kvm_lock_waiting *w = &per_cpu(lock_waiting, cpu);
+ if (ACCESS_ONCE(w->lock) == lock &&
+ ACCESS_ONCE(w->want) == ticket) {
+ add_stats(RELEASED_SLOW_KICKED, 1);
+ kvm_kick_cpu(cpu);
+ break;
+ }
+ }
+}
+
+/*
+ * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
+ */
+void __init kvm_spinlock_init(void)
+{
+ if (!kvm_para_available())
+ return;
+ /* Does host kernel support KVM_FEATURE_PV_UNHALT? */
+ if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
+ return;
+
+ printk(KERN_INFO "KVM setup paravirtual spinlock\n");
+
+ static_key_slow_inc(¶virt_ticketlocks_enabled);
+
+ pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
+ pv_lock_ops.unlock_kick = kvm_unlock_kick;
+}
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
On 08/06/2013 04:40 AM, Raghavendra K T wrote:> This series replaces the existing paravirtualized spinlock mechanism > with a paravirtualized ticketlock mechanism. The series provides > implementation for both Xen and KVM. > > The current set of patches are for Xen/x86 spinlock/KVM guest side, to be included > against -tip. >What is the baseline for this patchset? I tried to apply it on top of 3.11-rc4 and I got nontrivial conflicts. -hpa