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From: "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 09/18] virtio: use avail_event index
Date: Wed, 18 May 2011 08:43:40 +0300
Message-ID: <20110518054340.GE7589@redhat.com>
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Cc: Krishna Kumar <krkumar2-xthvdsQ13ZrQT0dZR+AlfA@public.gmane.org>, Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
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	Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
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	Christian Borntraeger <borntraeger-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
	Tom Lendacky <tahm-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
	Martin Schwidefsky <schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, linux390-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org
To: Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
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On Wed, May 18, 2011 at 09:49:42AM +0930, Rusty Russell wrote:
> On Tue, 17 May 2011 09:10:31 +0300, "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> > Well one can imagine a driver doing:
> > 
> > 	while (virtqueue_get_buf()) {
> > 		virtqueue_add_buf()
> > 	}
> > 	virtqueue_kick()
> > 
> > which looks sensible (batch kicks) but might
> > process any number of bufs between kicks.
> 
> No, we currently only expose the buffers in the kick, so it can only
> fill the ring doing that.
> 
> We could change that (and maybe that's worth looking at)...

Yes, I think we should - this way host and guest can process
data in parallel without a kick.

My patchset included that simply because it's one index
less to be confused about.


> > If we look at drivers closely enough, I think none
> > of them do the equivalent of the above, but not 100% sure.
> 
> I'm pretty sure we don't have this kind of 'echo' driver yet.  Drivers
> tend to take OS requests and queue them.  The only one which does
> anything even partially sophisticated is the net driver...
> 
> Thanks,
> Rusty.