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

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Message-ID: <OF35B7AA9F.54F10167-ON6525768F.0040BB45-6525768F.0040E28C@in.ibm.com>
Date:	Thu, 17 Dec 2009 17:29:55 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Jarek Poplawski <jarkao2@...il.com>, mst@...hat.com,
	netdev@...r.kernel.org, netdev-owner@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Sridhar Samudrala <sri@...ibm.com>
Subject: Re: [RFC PATCH] Regression in linux 2.6.32 virtio_net seen with	vhost-net

> Herbert Xu <herbert@...dor.apana.org.au>
> Sent by: netdev-owner@...r.kernel.org
>
> 12/17/2009 05:15 PM
>
> To
>
> Jarek Poplawski <jarkao2@...il.com>
>
> cc
>
> Krishna Kumar2/India/IBM@...IN, 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 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.

I think it is fine. The first skb after the stop is requeue'd. All
subsequent new skbs get screened out at qdisc_restart() -> dequeue_skb
-> NULL -> no work to do. Hope I didn't miss something now :-)

Thanks,

- KK

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