[Pw_forum] density files

[Paolo Giannozzi]

On Wednesday 08 February 2006 12:18, Silviu Zilberman wrote:

> I have been running calculations on Lemieux which is an alpha cluster
> super computer in Pittsburgh. For some reason that is still mysterious
> to me, writing these density files on the scratch space took very long
> time, ~30 (!) minutes for a 68MB file.

maybe you should rename your machine "Lepire" :-)

The charge density file should be written only when the wavefunctions
are written, every "isave" steps and at the end of the run. If it is written
at each time step, this is definitely wrong. 

The charge density in a parallel calculation is collected to a single node
and written from there. Since it is not wise to collect it into a single
array, each slice from each processor is collected and written. Maybe 
this algorithm is not optimal (maybe it is even "pessimal"). You should 
try to understand where exactly the machine spends all this time and
why

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
Piazza dei Cavalieri 7      I-56126 Pisa, Italy