[Pw_forum] Too many data communications between nodes when run pw.x in parallel?

[Axel Kohlmeyer]

On Tue, 30 Dec 2008, Wang Qinjing wrote:

QW> Dear all:

QW> I noted that if I made calculation by pw.x in paralllel, there were 
QW> too many data communications between nodes. That was attributed to 
QW> the data communication of wave functions. There is a severe delay to 
QW> get information from these nodes.

please provide more detail about the kind of job you 
are running, how you were running it and the kind of 
hardware you are running it on.

there are several ways how you can improve parallel efficiency.
please see the documentation and the many previous discussions
on this topic and then make some scaling and performance tests
to see how to run most efficiently. the best settings can vary
a lot between different inputs and calculation types.
 
QW> If I set disk_io='low', things are much better. But the main node 

this is only one option and indicates that you are most likely
not running your job in a very efficient manner.

QW> (or the first node) still has problem in net communication. I 
QW> noticed a charge density file is still written after each scf step. 
QW> Is that the problem?  Or is there anything I can do to improve this 
QW> situation?

there is a lot that can be done, but since you don't provide any
information on what you are already doing, it is impossible to
give any recommendation beyond urging you to (re-)read the 
documentation and FAQs.

cheers,
   axel.

QW> Thanks in advance.
QW> 
QW> Yours Wang
QW> 
QW> ------------------------------------
QW> ÍõÇؾµ£¬¸´µ©´óѧÎïÀíϵÑо¿Éú
QW> Wang Qinjing, Physics Department, 
QW> Fudan University

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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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