[Pw_forum] question on parallelism options and scaling factor

[pascal boulet]

Thanks Giovanni for your suggestion. I will send the scaling tests a 
sson as possible.

Regards
Pascal


Le 06/02/2013 10:24, Giovanni Pizzi a écrit :
> Dear Pascal,
> since you have more than one k-point, you could try to have each pool 
> within one node, so that only inter-pool communication occurs over 
> infiniband; for instance if you have 4 k-points you may try to use 4 
> pools on 4 nodes (or possibly 2 pools on 2 nodes, or 4 pools on 2 
> nodes, etc).
> This kind of parallelization should scale pretty well, if your system 
> allows it (i.e. you have  enough kpoints and your system fits in RAM). 
> Then, you can try to optimize the parallelization using the other 
> parallelization options.
>
> If you manage to do some scaling tests using the pools, could you 
> please report your results on this mailing list?
>
> Thanks, and best regards,
>
> Giovanni Pizzi
>
>
> On 02/05/2013 10:12 PM, pascal boulet wrote:
>> Dear all,
>>
>> I have a basic question about parallelism and scaling factor.
>>
>> First, I am running calculations on a cubic system with 58 atoms
>> (alat=19.5652  a.u.), 540 electrons (324 KS states) and few k-points
>> (4x4x4 grid=4 k-points), on 32 cores (4 nodes) but I can submit on many
>> more.
>>
>> I guess the best thing to do is to parallelize the calculation on the
>> bands but maybe also on the FFTs. We have an infiniband interconnection
>> network between the nodes.
>>
>> What would you suggest as values for image/pools/ntg/bands ?
>>
>> I have made a SCF test calculation on 16 and 32 cores. For the SCF cycle
>> (13 steps) I get the following timing:
>> For 16 cores: total cpu time spent up to now is    22362.4 secs
>> For 32 cores: total cpu time spent up to now is    17932.6 secs
>>
>> The speedup is "only" 25%. I would have expected a better speedup for
>> such a small number of cores. Am i wrong? What is your experience?
>>
>> (For additional information, if helpful: QE 5.0.1 has been compiled with
>> openMPI, intel 12.1 and FFTW 3.2.2.)
>>
>> thank you for your answers.
>>
>> Regards
>> Pascal
>>
>>
>>
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>
>
> -- 
> Giovanni Pizzi
> Post-doctoral Research Scientist
> EPFL STI IMX THEOS
> MXC 340 (Bâtiment MXC)
> Station 12
> CH-1015 Lausanne (Switzerland)
> Phone: +41 21 69 31124
>
>
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