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

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Message-ID: <4B29D36F.5000802@us.ibm.com>
Date:	Wed, 16 Dec 2009 22:45:03 -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 09:05:32PM -0800, Sridhar Samudrala wrote:
>   
>> 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.
>>     
>
> Yes but if the queue was stopped then we shouldn't even get into
> sch_direct_xmit.  
I don't see any checks for txq_stopped in the callers of sch_direct_xmit() :
__dev_xmit_skb() and qdisc_restart().  Both these routines get the txq 
and call
sch_direct_xmit() which checks if tx queue is stopped or frozen.

Am i missing something?

Thanks
Sridhar
> While inside sch_direct_xmit, then only way for
> the queue to be stopped is through dev_hard_start_xmit, and when
> that happens sch_direct_xmit will exit so we should never see a
> requeue if the driver is working properly.
>
> Cheers,
>   


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