[Bro] So uh...how do you know which pin_cpus to use?

Azoff, Justin S jazoff at illinois.edu
Tue Oct 18 13:55:56 PDT 2016


> On Oct 18, 2016, at 4:52 PM, Azoff, Justin S <jazoff at illinois.edu> wrote:
> 
> 
>> On Oct 18, 2016, at 4:34 PM, James Lay <jlay at slave-tothe-box.net> wrote:
>> 
>> Never really understood this:
>> 
>> "The correct pin_cpus setting to use is dependent on your CPU 
>> architecture. Intel and AMD systems enumerate processors in different 
>> ways. Using the wrong pin_cpus setting can cause poor performance."
>> 
>> Is there a magical formula?  Any advice would help thanks.
> 
> The best thing to do is to install the hwloc package and use the lstopo or lstopo-no-graphics tool to render a big ascii art image of the system.
> 
> 
> on centos7 this works:
> 
> lstopo-no-graphics  --of txt
> 
> 
> You'll get something that looks like this:
> 
> https://www.open-mpi.org/projects/hwloc/lstopo/images/2XeonE5v2+2cuda+1display_v1.11.png
> 
> or
> 
> https://www.open-mpi.org/projects/hwloc/lstopo/images/4Opteron6200.v1.11.png
> 
> The numbers towards the bottom are the cpu ids.  So you can see that using something like
> 
> 1,3,5,7,9,11,13,15,17,19,21,23,25
> 
> on an intel cpu would be the worst thing you could do since 21,23,25 are on the same physical cores as 1,3, and 5

Oh, I should add... ".. on that particular system".  On some of our numa machines the allocation is different and 1,3,5,7,9 would be the right cpus to use!

-- 
- Justin Azoff





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