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From "Farid Zaripov" <Farid_Zari...@epam.com>
Subject RE: atomic tests timing out on Windows
Date Thu, 26 Jul 2007 18:28:06 GMT
> -----Original Message-----
> From: Martin Sebor [mailto:msebor@gmail.com] On Behalf Of Martin Sebor
> Sent: Thursday, July 26, 2007 7:50 PM
> To: stdcxx-dev@incubator.apache.org
> Subject: Re: atomic tests timing out on Windows

> As I understand the technology, the benefit of hyperthreading 
> is in the processor's ability to make use of its idle 
> circuits while other circuits are busy doing things. But 
> because a HT processor does not actually duplicate most of 
> ordinary processor's circuits (I've seen 5% being tossed 
> around as the increase in the number of transistors between 
> an ordinary CPU and one with HT) it means that while one 
> thread that does FP processing can execute in parallel with 
> another that does integer arithmetic, two threads that are 
> doing the same thing cannot actually run simultaneously.
> 
> In our case, since both threads do exactly the same thing, 
> trying to run them on their own virtual "processors" 
> (emulated by HT) must make them run essentially serially just 
> as they would on an ordinary uniprocessor, and the scheduling 
> overhead involved in the OS and CPU switching between the two 
> threads must actually account for most of time spent by the process.
> 
> If my analysis is correct, we should avoid scheduling the 
> threads on multiple logical CPUs on HT systems with a single 
> physical CPU.
> Do you agree?

  I agree. Now we need to know how to determine if the CPU has
more than 1 logical CPU. And I think it is possible to make
machine with 2 HT-supporting CPU on board?

Here (http://www.intel.com/cd/ids/developer/asmo-na/eng/275339.htm)
I found the program with sources, that will help us.

Farid.

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