[Pw_forum] gipaw parallel run is too slow

[Ren PJ]

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

================================================
任鹏举
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