[QE-users] MPI & OpenMP - CPU and WALL TIME in QE 6.5

[Paolo Giannozzi]

Yes, it's the correct and expected behavior:
   wall time = time elapsed according to the clock on the wall
   CPU time= time spent in the CPU, summed over all threads
Paolo

On Wed, Mar 4, 2020 at 3:19 PM IORI, Federico <federico.iori at airliquide.com>
wrote:

> Dear all .
> I am doing some scalability test with MPI/OpenMP on QE 6.5 compile on
> IRENE skylake cluster at CEA (France).
> I noticed that (as in a past version of QE) I have an apparently  "weird"
> discrepancy between the WALL time and the CPU time at the end of the
> calculation.
>
> (QE 6.5 Intel 2017 + ELPA 2016 )
> 480 mpi processes * N_omp_threads:
>
> pw.out_480tasks_1omp:     PWSCF        :  20m54.92s CPU  21m47.65s WALL
> pw.out_480tasks_2omp:     PWSCF        :  28m 2.16s CPU  16m11.73s WALL
> pw.out_480tasks_3omp:     PWSCF        :  35m43.95s CPU  14m12.05s WALL
> pw.out_480tasks_4omp:     PWSCF        :  43m24.46s CPU  13m16.07s WALL
> pw.out_480tasks_5omp:     PWSCF        :  54m59.95s CPU  13m44.10s WALL
> pw.out_480tasks_6omp:     PWSCF        :      1h 1m CPU  12m33.37s WALL
> pw.out_480tasks_7omp:     PWSCF        :      1h12m CPU  13m28.96s WALL
> pw.out_480tasks_8omp:     PWSCF        :      1h19m CPU  12m41.74s WALL
>
> The WALL TIME seems to be the WALL TIME for 1 omp threads in every run.
> To that the CPU TIME = WALL TIME * N_omp_threads
>
> It this correct according to your experience or not?
> Thanks in advance.
> Best regards
>
>
> --
> Federico IORI
>
> Computational material scientist
>
> Paris Innovation Campus
>
> 1 chemin de la Porte des Loges
> <https://www.google.com/maps/place/Air+Liquide/@48.8297381,2.2016685,11.75z/data=%214m5%213m4%211s0x47e67e61a4fbbdc7:0xca3bea9e80059880%218m2%213d48.7630415%214d2.1333045>
> Les Loges en Josas – 78354 Jouy en Josas cedex
>
> Tel: +33(0) 6 72 03 66 19 - Mail: federico.iori at airliquide.com
>
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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