Date: Wed, 5 Dec 2007 21:03:43 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Jie Chen <chen@jlab.org>
Cc: Simon Holm Th??gersen <odie@cs.aau.dk>, Eric Dumazet <dada1@cosmosbay.com>,
       linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: Possible bug from kernel 2.6.22 and above, 2.6.24-rc4
Message-ID: <20071205200343.GA14570@elte.hu>
References: <4744ADA9.7040905@cosmosbay.com> <4744E0DC.7050808@jlab.org> <1195698770.11808.4.camel@odie.local> <4744F042.4070002@jlab.org> <20071204131707.GA4232@elte.hu> <4756C3D9.9030107@jlab.org> <20071205154014.GA6491@elte.hu> <4756D058.1070500@jlab.org> <20071205164723.GA25641@elte.hu> <4756E44E.8080607@jlab.org>
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* Jie Chen <chen@jlab.org> wrote:

> Since I am using affinity flag to bind each thread to a different 
> core, the synchronization overhead should increases as the number of 
> cores/threads increases. But what we observed in the new kernel is the 
> opposite. The barrier overhead of two threads is 8.93 micro seconds vs 
> 1.86 microseconds for 8 threads (the old kernel is 0.49 vs 1.86). This 
> will confuse most of people who study the 
> synchronization/communication scalability. I know my test code is not 
> real-world computation which usually use up all cores. I hope I have 
> explained myself clearly. Thank you very much.

btw., could you try to not use the affinity mask and let the scheduler 
manage the spreading of tasks? It generally has a better knowledge about 
how tasks interrelate.

	Ingo
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