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Subject: Re: [OMPI users] Best way to map MPI processes to sockets?
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-11-07 23:01:43


What Brice is saying is that hwloc is saying that your cores all have individual caches -- they're not shared. Have a look at a graphical hwloc output to see:

  lstopo mymachine.png

On Nov 7, 2012, at 7:17 PM, Brice Goglin wrote:

> What processor and kernel is this? (see /proc/cpuinfo, or run "lstopo
> -v" and look for attributes on the Socket line)
> You're hwloc output looks like an Intel Xeon Westmere-EX (E7-48xx or
> E7-88xx).
> The likwid output is likely wrong (maybe confused by the fact that
> hardware threads are disabled).
>
> Brice
>
>
>
>
> Le 07/11/2012 21:56, Blosch, Edwin L a écrit :
>>>>> In your desired ordering you have rank 0 on (socket,core) (0,0) and
>>>>> rank 1 on (0,2). Is there an architectural reason for that? Meaning
>>>>> are cores 0 and 1 hardware threads in the same core, or is there a
>>>>> cache level (say L2 or L3) connecting cores 0 and 1 separate from
>>>>> cores 2 and 3?
>> My thinking was that each MPI rank will be running 2 OpenMP threads and that there might be some benefit to having those threads execute on cores 0 and 1 because those cores might share some level of the memory hierarchy. No hardware threading is being used.
>>
>>>>> hwloc's lstopo should give you that information if you don't have that
>>>>> information handy.
>> Here you go, first likwid output then hwloc, just for the first socket.
>>
>> likwid output:
>> *************************************************************
>> Graphical:
>> *************************************************************
>> Socket 0:
>> +-----------------------------------------------------------------------------------------------------+
>> | +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ |
>> | | 0 | | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 9 | |
>> | +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+ |
>> | +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ |
>> | | 32kB | | 32kB | | 32kB | | 32kB | | 32kB | |
>> | +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ |
>> | +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ |
>> | | 256kB | | 256kB | | 256kB | | 256kB | | 256kB | |
>> | +-----------------+ +-----------------+ +-----------------+ +-----------------+ +-----------------+ |
>> | +-------------------------------------------------------------------------------------------------+ |
>> | | 30MB | |
>> | +-------------------------------------------------------------------------------------------------+ |
>> +-----------------------------------------------------------------------------------------------------+
>>
>> hwloc output:
>>
>> Machine (512GB)
>> NUMANode L#0 (P#0 64GB) + Socket L#0 + L3 L#0 (30MB)
>> L2 L#0 (256KB) + L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0 + PU L#0 (P#0)
>> L2 L#1 (256KB) + L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1 + PU L#1 (P#1)
>> L2 L#2 (256KB) + L1d L#2 (32KB) + L1i L#2 (32KB) + Core L#2 + PU L#2 (P#2)
>> L2 L#3 (256KB) + L1d L#3 (32KB) + L1i L#3 (32KB) + Core L#3 + PU L#3 (P#3)
>> L2 L#4 (256KB) + L1d L#4 (32KB) + L1i L#4 (32KB) + Core L#4 + PU L#4 (P#4)
>> L2 L#5 (256KB) + L1d L#5 (32KB) + L1i L#5 (32KB) + Core L#5 + PU L#5 (P#5)
>> L2 L#6 (256KB) + L1d L#6 (32KB) + L1i L#6 (32KB) + Core L#6 + PU L#6 (P#6)
>> L2 L#7 (256KB) + L1d L#7 (32KB) + L1i L#7 (32KB) + Core L#7 + PU L#7 (P#7)
>> L2 L#8 (256KB) + L1d L#8 (32KB) + L1i L#8 (32KB) + Core L#8 + PU L#8 (P#8)
>> L2 L#9 (256KB) + L1d L#9 (32KB) + L1i L#9 (32KB) + Core L#9 + PU L#9 (P#9)
>>
>> Thanks again
>>
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>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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