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

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Message-ID: <87tycsn9lt.fsf@rustcorp.com.au>
Date:	Wed, 18 May 2011 09:49:42 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
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 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)...

> 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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