From: "Michael S. Tsirkin" <mst@redhat.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: virtualization@lists.linux-foundation.org
Subject: Re: [PATCHv2] virtio: use smp_XX barriers on SMP
Date: Thu, 28 Jan 2010 15:37:08 +0200 [thread overview]
Message-ID: <20100128133708.GA3776@redhat.com> (raw)
In-Reply-To: <201001281001.09999.rusty@rustcorp.com.au>
On Thu, Jan 28, 2010 at 10:01:09AM +1030, Rusty Russell wrote:
> On Thu, 28 Jan 2010 09:12:23 am Michael S. Tsirkin wrote:
> > virtio is communicating with a virtual "device" that actually runs on
> > another host processor. Thus SMP barriers can be used to control
> > memory access ordering.
> >
> > Where possible, we should use SMP barriers which are more lightweight than
> > mandatory barriers, because mandatory barriers also control MMIO effects on
> > accesses through relaxed memory I/O windows (which virtio does not use)
> > (compare specifically smp_rmb and rmb on x86_64).
>
> Xen had a similar issue, in that UP guests running on SMP hosts need to issue
> SMP barriers. Is this not also a requirement for virtio?
Of course it is. That's why I have ifdef CONFIG_SMP and use
mandatory barriers on UP.
> But I'm not sure what came out of the discussion: Jeremy?
>
> Cheers,
> Rusty.
next prev parent reply other threads:[~2010-01-28 13:37 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-27 22:42 [PATCHv2] virtio: use smp_XX barriers on SMP Michael S. Tsirkin
2010-01-27 23:31 ` Rusty Russell
2010-01-28 13:37 ` Michael S. Tsirkin [this message]
2010-01-28 21:14 ` Rusty Russell
2010-01-29 11:27 ` Michael S. Tsirkin
2010-01-30 4:52 ` Rusty Russell
2010-01-29 13:48 ` Michael S. Tsirkin
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