linux-kernel - Re: [PATCH 09/18] virtio: use avail

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Message-ID: <20110518054340.GE7589@redhat.com>
Date:	Wed, 18 May 2011 08:43:40 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel@...r.kernel.org, Carsten Otte <cotte@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux390@...ibm.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Shirley Ma <xma@...ibm.com>, lguest@...ts.ozlabs.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-s390@...r.kernel.org, kvm@...r.kernel.org,
	Krishna Kumar <krkumar2@...ibm.com>,
	Tom Lendacky <tahm@...ux.vnet.ibm.com>, steved@...ibm.com,
	habanero@...ux.vnet.ibm.com
Subject: Re: [PATCH 09/18] virtio: use avail_event index

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@...hat.com> 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.
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