[Pw_forum] k-points parallelization in pwscf 4.2.1

[Gabriele Sclauzero]

On 02/14/2011 04:21 PM, Davide Sangalli wrote:
> OK. I think it could be a "memory - cache" related problem.
>
> I did the same test with lower cut-off (still 6 CPUs).
> Now my serial run used 0.2 % of the memory and my parallel around 1.3%
>
> The parallelization over the fft grid is still faster, but the kpts 
> parallelization now is faster than the serial run.
> Serial:                            PWSCF        :  1m 3.14s CPU 
> time,     1m 4.05s WALL time
> fft grid parallelization:   PWSCF        :      15.46s CPU time,       
>    16.36s WALL time
> kpts parallelization:       PWSCF        :      35.98s CPU time,      
>     36.47s WALL time
>
> Thank you and best regards,
> Davide


Maybe I didn't explain myself. I was referring to the complete timings, 
also with the separate contribution from all the subroutines.


GS

>
>
> On 02/14/2011 02:49 PM, Gabriele Sclauzero wrote:
>> Dear Davide,
>>
>>   it might be a memory-contention problem, since CPU cache sizes are 
>> of the order of a few MB. Please provide the detailed timings at the 
>> end of the runs (that are the first thing one should look at in order 
>> to interpret these kind of speedup tests).
>>
>> Next time please take a few seconds to sign your post using full name 
>> and affiliation.
>>
>> Regards,
>>
>> GS
>>
>>
>> Il giorno 14/feb/2011, alle ore 12.18, Davide Sangalli ha scritto:
>>
>>> Thank you for the answer.
>>>
>>> I did a check to be sure, but these jobs use only few MB of memory.
>>> The serial run uses just 2.5% of my node memory (so around 15% for the
>>> run on 6 CPUs).
>>> It does not seems to me that this could be the problem.
>>> Moreover in the fft parallelization the memory was not distributed 
>>> neither.
>>>
>>> Is it possible that pwscf is not properly compiled?
>>> Is there any other check that you would suggest to do?
>>>
>>> Best regards,
>>> Davide
>>>
>>> *************************************
>>>      Largest allocated arrays     est. size (Mb)     dimensions
>>>         Kohn-Sham Wavefunctions         5.68 Mb     (   6422,  58)
>>>         NL pseudopotentials            13.33 Mb     (   6422, 136)
>>>         Each V/rho on FFT grid          7.81 Mb     ( 512000)
>>>         Each G-vector array             1.76 Mb     ( 230753)
>>>         G-vector shells                 0.09 Mb     (  12319)
>>>      Largest temporary arrays     est. size (Mb)     dimensions
>>>         Auxiliary wavefunctions        22.73 Mb     (   6422, 232)
>>>         Each subspace H/S matrix        0.82 Mb     (    232, 232)
>>>         Each <psi_i|beta_j> matrix      0.12 Mb     (    136,  58)
>>>         Arrays for rho mixing          62.50 Mb     ( 512000,   8)
>>>      writing wfc files to a dedicated directory
>>>
>>>
>>> On 02/14/2011 11:34 AM, Paolo Giannozzi wrote:
>>>> Davide Sangalli wrote:
>>>>
>>>>> What could my problem be?
>>>> the only reason I can think of is that k-point parallelization doesn't
>>>> (and cannot) distribute memory, so the total memory requirement will
>>>> be npools*(size of serial execution). If you run on the same node six
>>>> instances of a large executable, memory conflicts may slow down more
>>>> than parallelization can speed up.
>>>>
>>>> P.
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>>
>>
>> § Gabriele Sclauzero, EPFL SB ITP CSEA
>> /   PH H2 462, Station 3, CH-1015 Lausanne/
>>
>>
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>
>
> Davide Sangalli
> MDM labs, IMM, CNR.
> Agrate (MI) Italy
>
>
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-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne

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