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Date: Wed, 22 Mar 2006 11:23:13 +0800
From: Erich Dollansky <oceanare AT pacific DOT net DOT sg>
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Subject: Re: pthreads don't scale on windows xp, but does scale on   linux,     cygwin 1.5.19
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Hi,

jdeifik wrote:
> At 07:00 PM 3/21/2006, you wrote:
> 
>> jdeifik wrote:
>>> I have a dual xeon 2.4ghz machine with hypertreading enabled.
>>> This gives me 4 logical processors.

> I am not sure why it is important to have a HT aware scheduler for 
> Windows, when there are 4 or more
> threads. I can see with 2 threads you would like to have one per 
> physical processor.
> With 4 or more threads, cygwin phtreads really sucks, 4->62%, 6->39%, 
> 8->30% efficiency.

I do not wonder. HT does not give a full CPU to the other thread. If the 
scheduler is not aware of the problem, it actually slows down the 
performance of the real CPU.
> 
> It seems to me that more and more apps are turning to threading for 
> performance,
> and more and more hardware is available with multi-processor, 
> multi-core, and multi-threading.

Yes, this is why programs must be written to run with real CPUs and not 
something Intel calls HyperThreading.

Erich

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