linux-kernel - Re: 'autogroup' sched code KILLING responsiveness

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Message-ID: <20110123185233.GA22378@rhlx01.hs-esslingen.de>
Date:	Sun, 23 Jan 2011 19:52:33 +0100
From:	Andreas Mohr <andi@...as.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Yong Zhang <yong.zhang0@...il.com>,
	Christian Kujau <christian@...dbynature.de>,
	Michael Witten <mfwitten@...il.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: 'autogroup' sched code KILLING responsiveness

> Christian, Michael, can you confirm that this and the second patch fixes the 
> interactivity bug for you? If yes then i'd like to apply and send this fix to Linus 
> ASAP.
> 
> Thanks,
> 
> 	Ingo

I'm currently running with autogroup enabled for the first time,
on Athlon XP -rc2 with _first patch only_ applied (saw second part too late),
and it appears to be working fine with some stress tests added
(multi-app benchmark, while... true, yes etc.).
Interestingly I had chosen to DISABLE the cgroup part of the scheduler
several months ago since it was slower than non-cgroup by quite some margin.

One should perhaps consider this issue to be evidence of a notable lack
of (possibly automated) test/usage coverage of UP configs
(together with the recent build error on UP that was discovered
once hitting -rc1 only, and not earlier!).

For this particular fix, perhaps the 0 vs. tg->shares change could be
followed up by a WARN_ON_ONCE() in some more internal non-hotpath function
if such a check is feasible in the current case.

Thanks,

Andreas Mohr
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