netdev - Re: [PATCHv2 10/14] virtio_net: limit xmit polling

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Message-ID: <8739k3k1fb.fsf@rustcorp.com.au>
Date:	Wed, 25 May 2011 11:05:04 +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: [PATCHv2 10/14] virtio_net: limit xmit polling

On Mon, 23 May 2011 14:19:00 +0300, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> I do understand how it seems a waste to leave direct space
> in the ring while we might in practice have space
> due to indirect. Didn't come up with a nice way to
> solve this yet - but 'no worse than now :)'

Let's just make it "bool free_old_xmit_skbs(unsigned int max)".  max ==
2 for the normal xmit path, so we're low latency but we keep ahead on
average.  max == -1 for the "we're out of capacity, we may have to stop
the queue".

That keeps it simple and probably the right thing...

Thanks,
Rusty.
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