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From: Willy Tarreau <w@1wt.eu>
To: Mike Galbraith <efault@gmx.de>
Cc: Olof Johansson <olof@lixom.net>,
	linux-kernel@vger.kernel.org,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@elte.hu>
Subject: Re: Scheduler(?) regression from 2.6.22 to 2.6.24 for short-lived threads
Date: Sat, 9 Feb 2008 09:03:20 +0100	[thread overview]
Message-ID: <20080209080319.GO8953@1wt.eu> (raw)
In-Reply-To: <1202543920.9578.3.camel@homer.simson.net>

Hi Mike,

On Sat, Feb 09, 2008 at 08:58:39AM +0100, Mike Galbraith wrote:
> 
> 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

How many CPUs do you have ? It's impressive to see such important variations.
I would guess from the numbers that you sometimes have 1 or 2 CPUs doing
nothing. I've already observed strange CPU usage patterns while building
kernels (bound to 50% usage on a dual-athlon), but I can't say for sure
that it was only on 2.6, so it may be related to make dependencies instead
(at least it's what I've been suspecting till now).

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

These ones look rather strange. What type of workload is it ? Can you
publish the program for others to test it ?

Regards,
Willy


  reply	other threads:[~2008-02-09  8:55 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-09  0:04 Olof Johansson
2008-02-09  0:08 ` Ingo Molnar
2008-02-09  0:32   ` Olof Johansson
2008-02-09  7:58 ` Mike Galbraith
2008-02-09  8:03   ` Willy Tarreau [this message]
2008-02-09 10:58     ` Mike Galbraith
2008-02-09 11:40       ` Willy Tarreau
2008-02-09 13:37         ` Mike Galbraith
2008-02-09 16:19           ` Willy Tarreau
2008-02-09 17:33             ` Mike Galbraith
2008-02-10  5:29             ` Olof Johansson
2008-02-10  6:15               ` Willy Tarreau
2008-02-10  7:00                 ` Olof Johansson
2008-02-10  7:58                   ` Willy Tarreau
2008-02-11  8:15                   ` Mike Galbraith
2008-02-11 17:26                     ` Olof Johansson
2008-02-11 19:58                       ` Mike Galbraith
2008-02-11 20:31                         ` Olof Johansson
2008-02-12  9:23                           ` Mike Galbraith
2008-02-13  5:49                             ` Mike Galbraith
2008-02-11 21:45               ` Bill Davidsen
2008-02-12  4:30                 ` Mike Galbraith
     [not found] <fa.6N2dhyJ1cmBqiuFKgCaYfwduM+0@ifi.uio.no>
2008-02-09  1:49 ` Robert Hancock

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