similar to: [PATCH] virtio_ring: use smp_store_mb

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

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

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 >

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 :-) Yes, we've recently established that xchg is indeed faster than mfence on at least recent machines,

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

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

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. > >

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. > >

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, Jul 11, 2018 at 10:27:10AM +0800, Tiwei Bie wrote: > This commit introduces the EVENT_IDX support in packed ring. > > Signed-off-by: Tiwei Bie <tiwei.bie at intel.com> Besides the usual comment about hard-coded constants like <<15: does this actually do any good for performance? We don't have to if we do not want to. > --- > drivers/virtio/virtio_ring.c |

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

On Thu, Dec 17, 2015 at 03:02:12PM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2015 at 03:26:29PM +0200, Michael S. Tsirkin wrote: > > > Note that virtio_mb() is weirdly inconsistent with virtio_[rw]mb() in > > > that they use dma_* ops for weak_barriers, while virtio_mb() uses > > > smp_mb(). > > > > It's a hack really. I think I'll clean it

On Thu, Dec 17, 2015 at 03:02:12PM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2015 at 03:26:29PM +0200, Michael S. Tsirkin wrote: > > > Note that virtio_mb() is weirdly inconsistent with virtio_[rw]mb() in > > > that they use dma_* ops for weak_barriers, while virtio_mb() uses > > > smp_mb(). > > > > It's a hack really. I think I'll clean it

On 2018?04?25? 13:15, Tiwei Bie wrote: > This commit introduces the event idx support in packed > ring. This feature is temporarily disabled, because the > implementation in this patch may not work as expected, > and some further discussions on the implementation are > needed, e.g. do we have to check the wrap counter when > checking whether a kick is needed? > >

On 2018?04?25? 13:15, Tiwei Bie wrote: > This commit introduces the event idx support in packed > ring. This feature is temporarily disabled, because the > implementation in this patch may not work as expected, > and some further discussions on the implementation are > needed, e.g. do we have to check the wrap counter when > checking whether a kick is needed? > >