[QE-users] q-e with `--enable-openmp' option doesn't give any performance boost, so should I set it or not for compiling?

[Hongyi Zhao]

Hi,

I try to compile the git master q-e on Ubuntu 20.04 using intel
parallel studio xe/2020.1.102 cluster version. The hardware is a dual
E5 * 2699v4 based machine. I tried with the following two different
configure options:

$ ./configure --with-scalapack=intel MPIF90=mpiifort --enable-openmp

or

$ ./configure --with-scalapack=intel MPIF90=mpiifort

For both cases, I set the (C|F)FLAGS to the following optimization
level: -O3 -xHost.

After the compilation, I try to test it with the example supplied
here: http://levilentz.com/Codes/BNDTutorial.tar.gz.

The test is based on the scf relax calculation from the above example,
as following:

$ mpirun -n 44 pw.x < relax.in > relax.out

But I find that the version compiled with `--enable-openmp' is more
time-consuming than the version without this option.

So, I'm very confused whether should I set the`--enable-openmp' option
for compiling q-e? Any hints for this problem will be highly
appreciated?
-- 
Hongyi Zhao <hongyi.zhao at gmail.com>