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

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Message-ID: <47570F83.6040601@jlab.org>
Date:	Wed, 05 Dec 2007 15:52:19 -0500
From:	Jie Chen <chen@...b.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Simon Holm Th??gersen <odie@...aau.dk>,
	Eric Dumazet <dada1@...mosbay.com>,
	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:
> 
>> I just disabled the affinity mask and reran the test. There were no 
>> significant changes for two threads (barrier overhead is around 9 
>> microseconds). As for 8 threads, the barrier overhead actually drops a 
>> little, which is good. Let me know whether I can be any help. Thank 
>> you very much.
> 
> sorry to be dense, but could you give me instructions how i could remove 
> the affinity mask and test the "barrier overhead" myself? I have built 
> "pthread_sync" and it outputs numbers for me - which one would be the 
> barrier overhead: Reference_time_1 ?
> 
> 	Ingo
Hi, Ingo:

To disable affinity, do configure --enable-public-release 
--disable-thread_affinity. You should see barrier overhead like the 
following:
Computing BARRIER time

Sample_size  Average     Min    Max          S.D.        Outliers
  20      19.486162   19.482250   19.491400    0.002740      0

BARRIER time =        19.486162 microseconds +/- 0.005371
BARRIER overhead =    8.996257 microseconds +/- 0.006575

The Reference_time_1 is the elapsed time for single thread doing simple 
loop without any synchronization. Thank you.

-- 
###############################################
Jie Chen
Scientific Computing Group
Thomas Jefferson National Accelerator Facility
12000, Jefferson Ave.
Newport News, VA 23606

(757)269-5046 (office) (757)269-6248 (fax)
chen@...b.org
###############################################

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