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Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb |
Date: |
Thu, 17 Dec 2015 16:34:57 +0200 |
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 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 <address@hidden>
> > 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.
Does outer coherent imply inner coherent?
> the *mb() primitives cover both.
Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb, Peter Zijlstra, 2015/12/17