similar to: [PATCH] sh: fix smp_store_mb for !SMP

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

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

On Thu, Dec 17, 2015 at 03:16:20PM +0200, Michael S. Tsirkin wrote: > On Thu, Dec 17, 2015 at 11:52:38AM +0100, Peter Zijlstra wrote: > > On Thu, Dec 17, 2015 at 12:32:53PM +0200, Michael S. Tsirkin wrote: > > > +static inline void virtio_store_mb(bool weak_barriers, > > > + __virtio16 *p, __virtio16 v) > > > +{ > > > +#ifdef CONFIG_SMP > >

On Thu, Dec 17, 2015 at 11:52:38AM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2015 at 12:32:53PM +0200, Michael S. Tsirkin wrote: > > +static inline void virtio_store_mb(bool weak_barriers, > > + __virtio16 *p, __virtio16 v) > > +{ > > +#ifdef CONFIG_SMP > > + if (weak_barriers) > > + smp_store_mb(*p, v); > > + else > > +#endif >

On Thu, Dec 17, 2015 at 11:52:38AM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2015 at 12:32:53PM +0200, Michael S. Tsirkin wrote: > > +static inline void virtio_store_mb(bool weak_barriers, > > + __virtio16 *p, __virtio16 v) > > +{ > > +#ifdef CONFIG_SMP > > + if (weak_barriers) > > + smp_store_mb(*p, v); > > + else > > +#endif >

Changes since v2: - extended checkpatch tests for barriers, and added patches teaching it to warn about incorrect usage of barriers (__smp_xxx barriers are for use by asm-generic code only), should help prevent misuse by arch code to address comments by Russell King - patched more instances of xen to use virt_ barriers as suggested by Stefano Stabellini - implemented a 2 byte xchg on sh

Changes since v2: - extended checkpatch tests for barriers, and added patches teaching it to warn about incorrect usage of barriers (__smp_xxx barriers are for use by asm-generic code only), should help prevent misuse by arch code to address comments by Russell King - patched more instances of xen to use virt_ barriers as suggested by Stefano Stabellini - implemented a 2 byte xchg on sh

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

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

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

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

On Thu, Dec 17, 2015 at 02:57:26PM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2015 at 03:16:20PM +0200, Michael S. Tsirkin wrote: > > On Thu, Dec 17, 2015 at 11:52:38AM +0100, Peter Zijlstra wrote: > > > On Thu, Dec 17, 2015 at 12:32:53PM +0200, Michael S. Tsirkin wrote: > > > > +static inline void virtio_store_mb(bool weak_barriers, > > > > +

On Thu, Dec 17, 2015 at 02:57:26PM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2015 at 03:16:20PM +0200, Michael S. Tsirkin wrote: > > On Thu, Dec 17, 2015 at 11:52:38AM +0100, Peter Zijlstra wrote: > > > On Thu, Dec 17, 2015 at 12:32:53PM +0200, Michael S. Tsirkin wrote: > > > > +static inline void virtio_store_mb(bool weak_barriers, > > > > +

On Wed, Dec 30, 2015 at 02:44:21PM +0100, Arnd Bergmann wrote: > On Wednesday 30 December 2015 15:24:47 Michael S. Tsirkin wrote: > > asm-generic variant of smp_store_mb() calls mb() which is stronger > > than implied by both the name and the documentation. > > > > smp_store_mb is only used by core kernel code at the moment, so > > we know no one mis-uses it for

asm-generic variant of smp_store_mb() calls mb() which is stronger than implied by both the name and the documentation. smp_store_mb is only used by core kernel code at the moment, so we know no one mis-uses it for an MMIO barrier. Make it call smp_mb consistently before some arch-specific code uses it as such by mistake. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> ---

On Wednesday 30 December 2015 15:24:47 Michael S. Tsirkin wrote: > asm-generic variant of smp_store_mb() calls mb() which is stronger > than implied by both the name and the documentation. > > smp_store_mb is only used by core kernel code at the moment, so > we know no one mis-uses it for an MMIO barrier. > Make it call smp_mb consistently before some arch-specific > code

On Wednesday 30 December 2015 15:24:47 Michael S. Tsirkin wrote: > asm-generic variant of smp_store_mb() calls mb() which is stronger > than implied by both the name and the documentation. > > smp_store_mb is only used by core kernel code at the moment, so > we know no one mis-uses it for an MMIO barrier. > Make it call smp_mb consistently before some arch-specific > code

We need a full barrier after writing out event index, using smp_store_mb there seems better than open-coding. As usual, we need a wrapper to account for strong barriers/non smp. 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> --- Seems to give a speedup

We need a full barrier after writing out event index, using smp_store_mb there seems better than open-coding. As usual, we need a wrapper to account for strong barriers/non smp. 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> --- Seems to give a speedup

On Thu, Dec 17, 2015 at 12:22:22PM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2015 at 12:32:53PM +0200, Michael S. Tsirkin wrote: > > Seems to give a speedup on my box but I'm less sure about this one. E.g. as > > xchng faster than mfence on all/most intel CPUs? Anyone has an opinion? > > Would help if you Cc people who would actually know this :-) Good point. Glad