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Re: [PATCH] virtio_ring: use smp_store_mb

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH] virtio_ring: use smp_store_mb
Date 2015-12-17 15:10 +0100
Message-ID <qGHpM-py-11@gated-at.bofh.it> (permalink)
References <qGE8x-6xd-9@gated-at.bofh.it> <qGEUW-79i-21@gated-at.bofh.it> <qGGN5-8nL-41@gated-at.bofh.it>
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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 up a bit to
> make it more consistent.
> 
> To simplify things, you may consider things before
> the optimization brought in by
> 	commit 9e1a27ea42691429e31f158cce6fc61bc79bb2e9
> 	Author: Alexander Duyck <alexander.h.duyck@redhat.com>
> 	Date:   Mon Apr 13 21:03:49 2015 +0930
> 
> 	    virtio_ring: Update weak barriers to use dma_wmb/rmb

That commit doesn't make any sense. dma_*mb() explicitly does _NOT_
cover the smp_*mb() part.

Again, look at the ARM definitions, the smp_*mb() primitives use the
inner coherence stuff, while the dma_*mb() primitives use the outer
coherent stuff.

the *mb() primitives cover both.
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[PATCH] virtio_ring: use smp_store_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-17 11:40 +0100
  Re: [PATCH] virtio_ring: use smp_store_mb Peter Zijlstra <peterz@infradead.org> - 2015-12-17 12:00 +0100
    Re: [PATCH] virtio_ring: use smp_store_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-17 14:20 +0100
      Re: [PATCH] virtio_ring: use smp_store_mb Peter Zijlstra <peterz@infradead.org> - 2015-12-17 15:00 +0100
        Re: [PATCH] virtio_ring: use smp_store_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-17 15:40 +0100
          Re: [PATCH] virtio_ring: use smp_store_mb Peter Zijlstra <peterz@infradead.org> - 2015-12-17 15:40 +0100
            Re: [PATCH] virtio_ring: use smp_store_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-17 15:50 +0100
            new barrier type for paravirt (was Re: [PATCH] virtio_ring: use  smp_store_mb) "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-20 10:30 +0100
              Re: [Xen-devel] new barrier type for paravirt (was Re: [PATCH]  virtio_ring: use smp_store_mb) Andrew Cooper <andrew.cooper3@citrix.com> - 2015-12-20 18:10 +0100
                Re: [Xen-devel] new barrier type for paravirt (was Re: [PATCH]  virtio_ring: use smp_store_mb) Peter Zijlstra <peterz@infradead.org> - 2015-12-20 21:10 +0100
                Re: [Xen-devel] new barrier type for paravirt (was Re: [PATCH]  virtio_ring: use smp_store_mb) "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-21 08:20 +0100
                [PATCH RFC] smp_store_mb should use smp_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-21 08:30 +0100
              Re: [Xen-devel] new barrier type for paravirt (was Re: [PATCH] virtio_ring:  use smp_store_mb) David Vrabel <david.vrabel@citrix.com> - 2015-12-21 11:50 +0100
                Re: [Xen-devel] new barrier type for paravirt (was Re: [PATCH]  virtio_ring: use smp_store_mb) "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-21 13:00 +0100
                Re: [Qemu-devel] [Xen-devel] new barrier type for paravirt (was Re:  [PATCH] virtio_ring: use smp_store_mb) Stefano Stabellini <stefano.stabellini@eu.citrix.com> - 2015-12-21 16:00 +0100
  Re: [PATCH] virtio_ring: use smp_store_mb Peter Zijlstra <peterz@infradead.org> - 2015-12-17 12:30 +0100
    Re: [PATCH] virtio_ring: use smp_store_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-17 14:30 +0100
      Re: [PATCH] virtio_ring: use smp_store_mb Peter Zijlstra <peterz@infradead.org> - 2015-12-17 15:10 +0100
        Re: [PATCH] virtio_ring: use smp_store_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-17 15:40 +0100
          Re: [PATCH] virtio_ring: use smp_store_mb Peter Zijlstra <peterz@infradead.org> - 2015-12-17 16:10 +0100
            Re: [PATCH] virtio_ring: use smp_store_mb Will Deacon <will.deacon@arm.com> - 2015-12-17 17:00 +0100
              Re: [PATCH] virtio_ring: use smp_store_mb "Michael S. Tsirkin" <mst@redhat.com> - 2015-12-17 20:30 +0100

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