[Pw_forum] parallel execution of PWscf

[Eduardo Ariel Menendez Proupin]

>I am using LG Quad core processor machine with PWscf running on linux. I
want to know >whether there is any command to run it parallely on the four
processors or by default with >simple installation (i.e.,  ./configure and
make all) it uses all the four processors?

It depends. configure detects your environment and set the options for an
optimal "compilation".

If you have MPI well installed, then configure detects it , and you run it
as Lorenzo explained (mpirun -np path-to-executables/pw.x )

There is another paralellism that you can exploit, although it is not from
espresso, but from the Intel MKL implementation of the BLAS/LAPACK
libraries. With ifort compiler (or other OpenMP capable compiler) and the
Intel MKL libraries well installed, configure detects the MKL and sets the
compilation options automatically to use the MKL. The MKL have OpenMP
parallelism implemented, and you run pw.x like a serial program, but the
matrix operations made by MKL libraries will run parallel. If it works, with
the command top you will see
CPU use higher than 100%, near 400 % if you have a QuadCore.

Take it into account if you compare performance of mpi vs "serial". When I
was unaware of the MKL built-in parallelism got unhappy because mpirun -np 2
pw.x (in a Dual Xeon) was only 30 % faster than just pw.x

Generally, this is slower than paralellization with MPI, but there is at
least one example where OpenMP runs faster.
http://www.democritos.it/pipermail/pw_forum/2008-May/008870.html
and
http://www.democritos.it/pipermail/pw_forum/2008-May/008884.html


If you have Intel or AMD CPU, try to compile espresso with the MKL. For
large calculations, the one for which speed is really important, using the
MKL can provide a factor of 5 in speed.

In summary,
If you just want to do fast calculations for small systems, do not care of
installing the parallel environment.
If you want to calculate large systems, take your time to study the manual.
After some training one can set the system to run efficiently in half a day,
i.e., install Fortran compiler, MKL libraries, MPI, ESPRESSO an do some
tests. Note that the latests distributions of Intel Fortran Compiler include
the MKl, then it is one step less.

Regards
Eduardo

---------- Mensaje reenviado ----------
> From: Neel Singh <neelphysics at yahoo.in>
> To: pw_forum at pwscf.org
> Date: Fri, 24 Jul 2009 17:06:10 +0530 (IST)
> Subject: [Pw_forum] parallel execution of PWscf
> Hi
> I am using LG Quad core processor machine with PWscf running on linux. I
> want to know whether there is any command to run it parallely on the four
> processors or by default with simple installation (i.e.,  ./configure and
> make all) it uses all the four processors?
>
> Neel
> University of Delhi
>
> ------------------------------
>
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