linux-kernel - Re: [patch] CFS scheduler, -v13

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Date:	Sun, 20 May 2007 08:38:04 +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>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Peter Williams <pwil3058@...pond.net.au>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch] CFS scheduler, -v13


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

> Hi Ingo,
> 
> 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. [...]

ah, great - i was looking over your debug data and couldnt find the 
problem! This moves CFS into the "no open regressions" state again ;-)

> [...] 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.

if that lag still occurs with rc2 then please repeat the following 
debugging steps under CFS [which has more instrumentation than the stock 
scheduler]:

  cat /proc/`pidof firefox-bin`/sched > sched1.txt
  echo 0 > /proc/`pidof firefox-bin`/sched

  < reproduce the lag in firefox >

  cat /proc/`pidof firefox-bin`/sched > sched2.txt

this way we'll be able to tell what nature this delay has. Also, could 
you send me your kernel's .config (off-list)?

	Ingo
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