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

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Message-ID: <475F0B07.2060303@jlab.org>
Date:	Tue, 11 Dec 2007 17:11:19 -0500
From:	Jie Chen <chen@...b.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Possible bug from kernel 2.6.22 and above, 2.6.24-rc4

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
> 
> 	Ingo
Hi, Ingo:

Yes, the extra 9 usecs overhead for running two threads in the 2.6.24 
kernel when there are total of 8 cores (2 quad opterons). What is the 
total number of cores do you have? I do not have machines that have dual 
quad Xeons here for direct comparisons. Thank you.

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