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

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Date:	Mon, 21 May 2007 09:58:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Anant Nitya <kernel@...chanda.info>
Cc:	linux-kernel@...r.kernel.org,
	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


* Anant Nitya <kernel@...chanda.info> wrote:

> Please ignore my last report about lag problem while using CFS-v13, it 
> is working perfectly fine with 2.6.21.1 and the lag I used to see in 
> v12 is not there with v13 anymore. After digging in a bit I found that 
> problem is only occurring in 2.6.22-rc1 and it get fired by network 
> usage while transmitting data upstream. I don't have any evidence that 
> CFS is involved in lag problem since 2.6.22-rc1 with stock scheduler 
> is also having same lag problem and it seems directly proportional 
> with upstream speed while downstream doesn't shows any misbehavior { 
> at lower upstream speed lag is less but with higher upstream speed 
> system starts crawling and system load hitting to 70/75}. Lets see how 
> 2.6.22-rc2 is doing.

ok, i got your -rc2 debug numbers (off-list), and it doesnt look pretty:

before-lag:

 sleep_max                :           259502076
 block_max                :            27690921
 wait_max                 :            16381558

after-lag:

 sleep_max                :           584186160
 block_max                :           261780071
 wait_max                 :           881255577

ouch! a nearly 1 second delay got observed by the scheduler - something 
is really killing your system!

what does 'top' show during an upload? Is any system related task out of 
whack? Could you try to get a readprofile or an oprofile output from the 
kernel, so that we can see what is slowing it down so much? It could be 
something networking related in v2.6.22-rc2.

	Ingo
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