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Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb
From: |
Peter Zijlstra |
Subject: |
Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb |
Date: |
Thu, 17 Dec 2015 12:22:22 +0100 |
User-agent: |
Mutt/1.5.21 (2012-12-30) |
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, see:
lkml.kernel.org/r/address@hidden
> +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
> + {
> + WRITE_ONCE(*p, v);
> + mb();
> + }
> +}
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().
As previously stated, smp_mb() does not cover the same memory domains as
dma_mb() would.
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, (continued)
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Peter Zijlstra, 2015/12/17
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Michael S. Tsirkin, 2015/12/17
- [Qemu-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring: use smp_store_mb), Michael S. Tsirkin, 2015/12/20
- Re: [Qemu-devel] [Xen-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring: use smp_store_mb), Andrew Cooper, 2015/12/20
- Re: [Qemu-devel] [Xen-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring: use smp_store_mb), Peter Zijlstra, 2015/12/20
- Re: [Qemu-devel] [Xen-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring: use smp_store_mb), Michael S. Tsirkin, 2015/12/21
- [Qemu-devel] [PATCH RFC] smp_store_mb should use smp_mb, Michael S. Tsirkin, 2015/12/21
- Re: [Qemu-devel] [Xen-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring: use smp_store_mb), David Vrabel, 2015/12/21
- Re: [Qemu-devel] [Xen-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring: use smp_store_mb), Michael S. Tsirkin, 2015/12/21
- Re: [Qemu-devel] [Xen-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring: use smp_store_mb), Stefano Stabellini, 2015/12/21
Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb,
Peter Zijlstra <=
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Michael S. Tsirkin, 2015/12/17
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Peter Zijlstra, 2015/12/17
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Michael S. Tsirkin, 2015/12/17
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Peter Zijlstra, 2015/12/17
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Will Deacon, 2015/12/17
- Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Michael S. Tsirkin, 2015/12/17