cp2k.ssmp maximum number of threads?

[Alfio Lazzaro]

Dear Vedran,
as Juerg already said, we don't set any maximum on the number of threads 
(anywhere) in CP2K. We use the OpenMP runtime mechanism to check the number 
of threads. You can check the number of threads that CP2K is using in the 
following line of the output (at the very beginning of the CP2K execution):

GLOBAL| Number of threads for this process 
                                  18

If you observe any change when you compile on a machine and execute on 
another, then it is not CP2K related (I can guess that it is due to OpenMP 
runtime...).

I wonder how you are checking the number of threads that are used in CP2K 
during the execution. Do you use htop (or something similar) or you look at 
the performance scaling? I can tell you that OpenMP parallelization in CP2K 
is not optimal for several reasons (memory access, limited algorithm 
scaling...). In general, we see a limit around 4 threads (however, this is 
really algorithm-dependent and I don't know what you are running!), 
therefore we suggest using a combination of MPI and OpenMP (PSMP version). 
There is an ongoing effort on improving the OpenMP performance, but it will 
take some time... You are welcome to contribute :)

Alfio


Il giorno lunedì 27 novembre 2017 15:59:24 UTC+1, Vedran Miletić ha scritto:
>
> Hello,
>
> is there a maximum number of threads that cp2k.ssmp will use? I have been 
> trying small systems (2-5 heavy atoms), but it doesn't go above 8 threads 
> on a dual-CPU 16-core 32-thread machine.
>
> Thanks,
> Vedran
>
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