[Pw_forum] gipaw parallel run is too slow

Ren PJ renpj at dicp.ac.cn
Fri Nov 18 12:34:42 CET 2011

On Fri, 18 Nov 2011 10:54:56 +0100

> Dear Pengju Ren,
> when you increase the numebr of processors you increase the
> available computing power, but also the amount of communications on
> the network connectign those nodes. As the network has a finite
> speed, there will be a point where the code looses more time
> exchanging information between the cpus than doing any calculation.
> Possible solutions:
> 1. use fewer cpus (between 8 and 160 there is plenty of space)
> 2. try with a different number of pools (you could try  
> nkpoints*ncores_per_node)
> 3. buy some faster network hardware
> best regards

Dear Lorenzo Paulatto,
Thanks for your kind answer.
When I ran pw.x with 160 cpus it was about 10 times faster than with 8
cpus, I think the parallel efficiency is reasonable. So does gipaw.x
need more communications between nodes than pw.x? Maybe the gipaw code
could be improved by reducing the communication frequency.

Best Wishes

Pengju Ren
renpj at dicp.ac.cn
State  Key Laboratory of Catalysis, 
Dalian Institute of Chemical Physics, 
Chinese Academy of Sciences 
457 zhongshan Road, Dalian, 116023, P.R. China  

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