linux-kernel - Re: Possible bug from kernel 2.6.22 and above, 2.6.24-rc4

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Date:	Wed, 12 Dec 2007 13:49:06 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jie Chen <chen@...b.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: Possible bug from kernel 2.6.22 and above, 2.6.24-rc4


On Tue, 2007-12-11 at 17:11 -0500, Jie Chen wrote:
> Ingo Molnar wrote:
> > * Jie Chen <chen@...b.org> wrote:
> > 
> >> The following is pthread_sync output for 2.6.21.7-cfs-v24 #1 SMP 
> >> kernel.
> > 
> >> 2 threads:
> > 
> >> PARALLEL time =       11.106580 microseconds +/- 0.002460
> >> PARALLEL overhead =    0.617590 microseconds +/- 0.003409
> > 
> >> Output for Kernel 2.6.24-rc4 #1 SMP
> > 
> >> PARALLEL time =              19.668450 microseconds +/- 0.015782
> >> PARALLEL overhead =           9.157945 microseconds +/- 0.018217
> > 
> > ok, so the problem is that this PARALLEL time has an additional +9 usecs 
> > overhead, right? I dont see this myself on a Core2 CPU:
> > 
> > PARALLEL time =                           10.446933 microseconds +/- 0.078849
> > PARALLEL overhead =                       0.751732 microseconds +/- 0.177446
> > 

On my dual socket AMD Athlon MP

2.6.20-13-generic

PARALLEL time =                           22.751875 microseconds +/- 21.370942
PARALLEL overhead =                       7.046595 microseconds +/- 24.370040

2.6.24-rc5

PARALLEL time =                           17.365543 microseconds +/- 3.295133
PARALLEL overhead =                       2.213722 microseconds +/- 4.797886



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