[Insight-developers] how can I verify that my code runs on several processors ?

[Gaetan Lehmann]

The server contains 4 xeons with hyperthreading activated.
The hyperthreading is a part of my problem: I don't know how I can be sure  
that 2 threads are not running on the same processor. I see 8 processors,  
and I don't know how the CPU numbers are given, so I can't be sure my  
thread are not running on the same real CPU.

But I'm not sure that the lone problem: I get worst and worst performance  
when I increase the number of threads (up to 4) - it seems very similar to  
what I get on a single processor system. I think I should get a (small)  
increase of performance when the number of thread increase

On Mon, 28 Nov 2005 16:24:52 +0100, Kent Williams  
<norman-k-williams at uiowa.edu> wrote:

> I don't know what processors your server contains, but it's not always  
> the case that multithreading increases performance.  Intel HT processors  
> in particular have problems with too many shared resources between the  
> computation units.  The following article indicates that SQL Server and  
> Citrix Terminal Server both perform better with hyperthreading disabled.
>
> http://news.zdnet.co.uk/0,39020330,39237341,00.htm
>
> I don't know how you can verify that your threads are being spread  
> across different processors on your server -- perhaps someone else here  
> does.   ITK's threading model generally works very well, but there may  
> be cases where it does not.  For some cases -- particularly short,  
> simple ITK pipelines -- threading has minimal positive, and possibly  
> negative impact on performance.
>
> Gaetan Lehmann wrote:
>
>>
>> Hi,
>>
>> I'm trying to measure the performances of the filter I'm writing on a   
>> server with 4 processors. I'm quite surprise to see that using several   
>> threads seem to decrease the performances, as it do on a host with a   
>> single processor.
>> How can I verify that the different threads are running on several   
>> processors ? It's not fully related to ITK, but I hope someone will be   
>> able to answer that question on this list :-)
>>
>> I'm running my tests on linux.
>>
>> Thanks,
>>
>> Gaetan
>>
>>
>



-- 
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://voxel.jouy.inra.fr