linux-kernel - Re: Performance loss 2.6.22->22.6.23->2.6.24-rc7 on CPU intensive benchmark on 8 Core Xeon

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Date:	Wed, 16 Jan 2008 17:19:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Colin Fowler <elethiomel@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Performance loss 2.6.22->22.6.23->2.6.24-rc7 on CPU intensive
	benchmark on 8 Core Xeon

* Colin Fowler <elethiomel@...il.com> wrote:

> Hi Ingo, I'll need to convince my supervisor first if I can release a 
> binary. Technically anythin glike this needs to go through our 
> University's "innovations department" and requires lengthy paperwork 
> and NDAs :(.

a binary wouldnt work for me anyway. But you could try to write a 
"workload simulator": just pick out the pthread ops and replace the 
worker functions with some dummy stuff that just touches an array that 
has similar size to the tiles (in a tight loop). Make sure it has 
similar context-switch rate and idle percentage as your real workload - 
then send us the .c file. As long as it's a single .c file that runs for 
a few seconds and outputs a precise enough "run time" result, kernel 
developers would pick it up and use it for optimizations. To get the # 
of cpus automatically you can do:

        cpus = system("exit `grep processor /proc/cpuinfo  | wc -l`");
        cpus = WEXITSTATUS(cpus);

and start as many threads as many CPUs there are in the system.

	Ingo
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