Increasing nb of cores per node degrade drastically the performance of cp2k.popt

Shadrina Maria shadr... at
Tue Jul 12 19:51:13 UTC 2011

Dear All,

I've started to use cp2k and noticed that job is slowed down on 2x8 procs in
comparison with 2x2.
We compared CPU timing per opt step for QM/MM task:

 nodes x cores/node   CPU time per iter, sec

2x2          115

1x4          108

4x2            70

1x8            82

2x8         4500

4x8         4200

Using of TRACE setting revealed that problem is mainly in cp_fm_syevd_base
subroutine which spent almost all of this additional CPU time in 2x8 and 4x8

And we also compared CPU times of test 32H2O-md.inp for 2x2 and 2x8 cases
and got:

 nodes x cores/node   CPU time per iter, sec

2x2          33

2x8          172

TRACE revealed that qs_forces,  qs_energies_scf,  scf_env_do_scf,
velocity_verlet,  qs_forces,  qs_energies_scf,   scf_env_do_scf and others
are 5 times slower in 2x8 than 2x2

Do you have any suggections and ideas why it's happened?

CP2K version 2.2.262
the lib is MKL-Scalapack
the system is cluster of XEON nodes (8cores/node) with Infiniband switch
the compiler is Intel's

Thank you in advance.
Best regards, Maria.
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