netdev - Re: [RFC PATCH] Regression in linux 2.6.32 virtio

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Message-ID: <20091217114937.GA30503@gondor.apana.org.au>
Date:	Thu, 17 Dec 2009 19:49:37 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Krishna Kumar2 <krkumar2@...ibm.com>,
	Sridhar Samudrala <sri@...ibm.com>, mst@...hat.com,
	netdev@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH] Regression in linux 2.6.32 virtio_net seen with
	vhost-net

On Thu, Dec 17, 2009 at 07:45:35PM +0800, Herbert Xu wrote:
> On Thu, Dec 17, 2009 at 11:27:55AM +0000, Jarek Poplawski wrote:
> >
> > So we _should_ get into sch_direct_xmit when the queue was stopped...
> > I guess Herbert might forget the multiqueue change, and Sridhar isn't
> > missing much. ;-)
> 
> Hmm, if that's the case then this new multiqueue code is seriously
> broken.  It means that once the queue is stopped, every new tx packet
> will cause an unnecessary dequeue/requeue, up to 1000.

And indeed, this new requeue behaviour was introduced in 2.6.32.

Sridhar, please build the 2.6.32 virtio-net driver under a 2.6.31
kernel and see if the regression persists.  Alternatively, build
the virtio-net driver under 2.6.32 and see whether it still performs
as well.

Thanks,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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