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

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Message-Id: <1202543920.9578.3.camel@homer.simson.net>
Date:	Sat, 09 Feb 2008 08:58:39 +0100
From:	Mike Galbraith <efault@....de>
To:	Olof Johansson <olof@...om.net>
Cc:	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 Fri, 2008-02-08 at 18:04 -0600, Olof Johansson wrote:
> Hi,
> 
> I ended up with a customer benchmark in my lap this week that doesn't
> do well on recent kernels. :(
> 
> After cutting it down to a simple testcase/microbenchmark, it seems like
> recent kernels don't do as well with short-lived threads competing
> with the thread it's cloned off of. The CFS scheduler changes come to
> mind, but I suppose it could be caused by something else as well.
> 
> The pared-down testcase is included below. Reported runtime for the
> testcase has increased almost 3x between 2.6.22 and 2.6.24:
> 
> 2.6.22: 3332 ms
> 2.6.23: 4397 ms
> 2.6.24: 8953 ms
> 2.6.24-git19: 8986 ms

My 3GHz P4 shows disjointed results.

2.6.22.17-smp
time 798 ms
time 780 ms
time 702 ms

2.6.22.17-cfs-v24.1-smp
time 562 ms
time 551 ms
time 551 ms

2.6.23.15-smp
time 254 ms
time 254 ms
time 293 ms

2.6.23.15-cfs-v24-smp
time 764 ms
time 791 ms
time 780 ms

2.6.24.1-smp
time 815 ms
time 820 ms
time 771 ms

2.6.25-smp (git today)
time 29 ms
time 61 ms
time 72 ms


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