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

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Date:	Wed, 16 Dec 2009 21:05:32 -0800
From:	Sridhar Samudrala <sri@...ibm.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	Rusty Russell <rusty@...tcorp.com.au>, mst@...hat.com,
	netdev@...r.kernel.org
Subject: Re: [RFC PATCH] Regression in linux 2.6.32 virtio_net seen with vhost-net

Herbert Xu wrote:
> On Wed, Dec 16, 2009 at 05:43:00PM -0800, Sridhar Samudrala wrote:
>   
>> I had to change virtnet_xmit_poll() to get it working. See below.
>> With this change, i don't see any 'queue full' warnings, but requeues
>> are still happening at the qdisc level (sch_direct_xmit() finds that
>> tx queue is stopped and does requeues).
>>     
>
> Actually this makes no sense.  The queue should only be stopped
> at the end of a xmit run, in which case sch_direct_xmit should
> return 0 so we should never see a requeue.
>   
I think sch_direct_xmit() is not even calling dev_hard_start_xmit() as 
the tx queue is stopped
and does a dev_requeue_skb() and returns NETDEV_TX_BUSY.

> So if we're still seeing requeues then it hasn't been fixed
> properly.
>
> Cheers,
>   


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