[Pw_forum] scalability of the code

[Paolo Giannozzi]

On Tue, 2012-02-07 at 09:38 +0100, giacsport at libero.it wrote:

> I would like to know which is the highest number of processors
> used and reported for running PWscf code.

I have seen a test run on 65536 processors (cores, I mean).
Unfortunately I do not find any longer a test on a 8000-atom 
system recently done: I guess it was also run on more than 
just a few processors.

> Are there data or reports on the scalability of the code (well) 
> above 1000 processors?

there is something in the Benchmark section of the new web site
( http://testwp.qe-forge.it/wordpress-3.1.4/?page_id=44 ). 
More data will (maybe) come (subject to my allergy to both benchmarks 
and wordpress, and to everybody's allergy to documentation)

> We are indeed interested in installing the code in a massively parallel 
> machine, but before doing it we would like to have more information.

QE has been installed (with little effort) on several BlueGene machines.
It works (i.e. it has ben used for real scientific purposes and has
produced published results in at least one case I am aware of). You 
have to be careful with I/O, which can become easily a limiting factor.
You may need to use all available parallelization levels, in particular
OpenMP, to satisfy the machine owners who, for sure, wants you to run 
on a number of cores vastly exceeding what you actually need

P. 
-- 
Paolo Giannozzi, IOM-Democritos and University of Udine, Italy