[QE-users] QE 6.4 - slower with intel fftw? how to properly benchmark

[Christoph Wolf]

Dear all,

please forgive this "beginner" question but I am facing a weird problem.
When compiling qe-6.4 (intel compiler, intel MPI+OpenMP) with or without
intel's fftw libs I find that in openMP with 2 threads per core the intel
fftw version is roughly "twice as slow" as the internal one

"internal"
     General routines
     calbec       :      2.69s CPU      2.70s WALL (     382 calls)
     fft          :      0.47s CPU      0.47s WALL (     122 calls)
     ffts         :      0.05s CPU      0.05s WALL (      12 calls)
     fftw         :     49.97s CPU     50.12s WALL (   14648 calls)

     Parallel routines

     PWSCF        :  1m45.03s CPU     1m46.59s WALL

"intel fftw"
     General routines
     calbec       :      6.36s CPU      3.20s WALL (     382 calls)
     fft          :      0.93s CPU      0.47s WALL (     121 calls)
     ffts         :      0.10s CPU      0.05s WALL (      12 calls)
     fftw         :    109.63s CPU     55.23s WALL (   14648 calls)

     Parallel routines

     PWSCF        :   3m18.32s CPU   1m41.01s WALL

as a benchmark I am running a perovskite with 120 k-points on 30 processors
(one node); There is no (noticeable) difference if I export
OMP_NUM_THREADS=1 (only MPI) so I guess I made some mistake during the
build with regards to the libraries.

Build process is as below

module load intel19/compiler-19

module load intel19/impi-19


export FFT_LIBS="-L$MKLROOT/intel64"

export LAPACK_LIBS="-lmkl_blacs_intelmpi_lp64"

export CC=icc FC=ifort F77=ifort MPIF90=mpiifort MPICC=mpiicc


./configure --enable-parallel --with-scalapack=intel --enable-openmp


This detects BLAS_LIBS, LAPACK_LIBS, SCALAPACK_LIBS and FFT_LIBS.

I am not experienced with benchmarking so if my benchmark is garbage please
suggest a suitable system!

Thanks in advance!
Chris

-- 
Postdoctoral Researcher
Center for Quantum Nanoscience, Institute for Basic Science
Ewha Womans University, Seoul, South Korea
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