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Re: [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers
Date: Thu, 1 Sep 2011 18:30:21 +0300
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, Sep 01, 2011 at 04:09:49PM +1000, David Gibson wrote:
> The virtio code already has memory barrier wmb() macros in the code.
> However they are was defined as no-ops.  The comment claims that real
> barriers are not necessary because the code does not run concurrent.
> However, with kvm and io-thread enabled, this is not true and this qemu
> code can indeed run concurrently with the guest kernel.  This does not
> cause problems on x86 due to it's strongly ordered storage model, but it
> causes a race leading to virtio errors on POWER which has a relaxed storage
> ordering model.

Why not limit the change to ppc then?


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