linux-kernel - Re: [PATCH 2/5] virtio: support unlocked queue kick

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Message-ID: <20111006131828.GC19023@redhat.com>
Date:	Thu, 6 Oct 2011 11:19:18 -0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Jens Axboe <axboe@...nel.dk>,
	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] virtio: support unlocked queue kick

On Thu, Oct 06, 2011 at 12:15:36PM +1030, Rusty Russell wrote:
> On Wed, 05 Oct 2011 15:54:05 -0400, Christoph Hellwig <hch@...radead.org> wrote:
> > Split virtqueue_kick to be able to do the actual notification outside the
> > lock protecting the virtqueue.  This patch was originally done by
> > Stefan Hajnoczi, but I can't find the original one anymore and had to
> > recreated it from memory.  Pointers to the original or corrections for
> > the commit message are welcome.
> 
> An alternative to this is to update the ring on every virtqueue_add_buf.
> MST discussed this for virtio_net, and I think it's better in general.
> 
> The only reason that it wasn't written that way originally is that the
> barriers make add_buf slightly more expensive.
> 
> Cheers,
> Rusty.

With event index, I'm not sure that's enough to make the kick lockless
anymore.


-- 
MST
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