linux-kernel - Re: [PATCH] virtio_ring: use smp_store

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Message-ID: <20151217150917.GP6373@twins.programming.kicks-ass.net>
Date:	Thu, 17 Dec 2015 16:09:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Jason Wang <jasowang@...hat.com>, qemu-devel@...gnu.org,
	Alexander Duyck <alexander.duyck@...il.com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] virtio_ring: use smp_store_mb

On Thu, Dec 17, 2015 at 04:34:57PM +0200, Michael S. Tsirkin wrote:
> On Thu, Dec 17, 2015 at 03:02:12PM +0100, Peter Zijlstra wrote:

> > > 	commit 9e1a27ea42691429e31f158cce6fc61bc79bb2e9
> > > 	Author: Alexander Duyck <alexander.h.duyck@...hat.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.
> 
> Does outer coherent imply inner coherent?
> 
> > the *mb() primitives cover both.

I do not think so, but lets add Will, he dreams this stuff.
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