linux-kernel - Re: Scheduler(?) regression from 2.6.22 to 2.6.24 for short-lived threads

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Message-Id: <1202881762.27877.5.camel@homer.simson.net>
Date:	Wed, 13 Feb 2008 06:49:22 +0100
From:	Mike Galbraith <efault@....de>
To:	Olof Johansson <olof@...om.net>
Cc:	Willy Tarreau <w@....eu>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Scheduler(?) regression from 2.6.22 to 2.6.24 for short-lived
	threads


On Tue, 2008-02-12 at 10:23 +0100, Mike Galbraith wrote:

> If you plunk a usleep(1) in prior to calling thread_func() does your
> testcase performance change radically?  If so, I wonder if the real
> application has the same kind of dependency.

The answer is yes for 2.6.22, and no for 2.6.24, which surprised me.

2.6.22.17-smp
homer:..local/tmp # ./threadtest2
10000000 loops time 16215 ms
10000000 loops time 16268 ms
10000000 loops time 16246 ms

homer:..local/tmp # ./threadtest3 (with usleep(1))
10000000 loops time 13938 ms
10000000 loops time 13921 ms
10000000 loops time 13898 ms

2.6.24.1-smp
homer:..local/tmp # ./threadtest2
10000000 loops time 14663 ms
10000000 loops time 14523 ms
10000000 loops time 14466 ms

homer:..local/tmp # ./threadtest3
10000000 loops time 14513 ms
10000000 loops time 14500 ms
10000000 loops time 14464 ms

echo 0 >  /proc/sys/kernel/sched_child_runs_first

homer:..local/tmp # ./threadtest2
10000000 loops time 14157 ms
10000000 loops time 14097 ms
10000000 loops time 14153 ms

homer:..local/tmp # ./threadtest3
10000000 loops time 14065 ms
10000000 loops time 14075 ms
10000000 loops time 14018 ms



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