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

From: Michael S. Tsirkin
Date: Thu Oct 06 2011 - 05:18:39 EST

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@xxxxxxxxxxxxx> 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

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