linux-kernel - Re: bad networking related lag in v2.6.22-rc2

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Date:	Tue, 22 May 2007 01:10:13 +0530
From:	Anant Nitya <kernel@...chanda.info>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: bad networking related lag in v2.6.22-rc2

On Monday 21 May 2007 13:42:01 Ingo Molnar wrote:
> * Ingo Molnar <mingo@...e.hu> wrote:
> > > ouch! a nearly 1 second delay got observed by the scheduler - something
> > > is really killing your system!
> >
> > ah, you got the latency tracer from Thomas, as part of the -hrt patchset
> > - that makes it quite a bit easier to debug. [...]
>
> and ... you already did a trace for Thomas, for the softirq problem:
>
>    http://cybertek.info/taitai/trace.txt.bz2
>
> this trace shows really bad networking related kernel activities!
>
> gkrellm-5977 does this at timestamp 0:
>
>  gkrellm-5977  0..s.    0us : cond_resched_softirq (established_get_next)
>
> 2 milliseconds later it's still in established_get_next() (!):
>
>  gkrellm-5977  0..s. 2001us : cond_resched_softirq (established_get_next)
>
> and the whole thing takes ... 455 msecs:
>
>  gkrellm-5977  0..s. 455443us+: cond_resched_softirq (established_get_next)
>
> i think this suggests that you have tons of open sockets. What does
> "netstat -ts" say on your box?
I am posting links to the information you asked for. One more thing, after 
digging a bit more I found its QoS shaping that is making the box crawl. Once 
I disabled the traffic shaping everything comes back to smooth and normal. 
Shaping being done on very low speed residential ADSL 256/64 Kbps connection.
If you want me to post shaping rules, please free to ask. BTW its a simple 
HTB/SFQ rules.

http://cybertek.info/taitai/netstat-ts-before-crawl-normal-workload.txt
http://cybertek.info/taitai/netstat-ts-while-crawl-normal-workload.txt
http://cybertek.info/taitai/trace-to-ingo.txt.bz2

Regards
Ananitya
>
> 	Ingo



-- 
Out of many thousands, one may endeavor for perfection, and of
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