linux-kernel - Re: NET_SCHED cbq dropping too many packets on a bonding interface

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Message-ID: <20080515180914.GA2936@ami.dom.local>
Date:	Thu, 15 May 2008 20:09:14 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Kingsley Foreman <kingsley@...ernode.com.au>,
	Eric Dumazet <dada1@...mosbay.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: NET_SCHED cbq dropping too many packets on a bonding interface

On Thu, May 15, 2008 at 06:09:36PM +0200, Patrick McHardy wrote:
> Kingsley Foreman wrote:
>> i just rolled back the kernel to 2.6.24 and im seeing the same thing,
>>
>> I was using 2.6.22 before and didn't see the problem, txqueuelen on the 
>> bond0 interface is 0 (the default)
>
> That might explain things, although it shouldn't have worked before
> either.
>
> CBQ creates default pfifo qdiscs for its leaves, these use a limit
> of txqueuelen or 1 if it is zero. So even small bursts will cause
> drops. Do things improve if you set txqueuelen to a larger value
> *before* configuring the qdiscs?

Kingsley wrote to me that even after changing txqueuelen to 1000 the
"dropped" number didn't change much. A debugging patch with printks
around all "sch->qstats.dropps++" showed only the end of cbq_enqueue().
I've asked to check tomorrow "pfifo limit 1000" for these drops too.

> Another thing is that CBQ on bond will probably not work properly
> at all, it needs a real device since it measures the timing between
> dequeue events for idle time estimation. On software devices this
> doesn't work.

Right, but these drops without any sign of overactions or overlimits
seem to show it's not about shaping (or it's not counted/documented
enough).

Regards,
Jarek P.
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