[CP2K-user] [CP2K:12238] Running Cp2k in parallel using thread in a PC

[Pierre Cazade]

Hello Nikhil,

Withe command "mpirun -n 42 cp2k.pop -i inp.inp -o -out.out", you are 
requesting 42 MPI threads and not 42 OpenMP threads. MPI usually relies 
on replicated data which means that, for a poorly program software, it 
will request a total amount of memory which the amount of memory 
required by a scalar execution times the number of threads. This can 
very quickly become problematic, in particular for QM calculations. 
OpenMP, however relies on shared memory, the data is normally not 
replicated but shared between threads and therefore, in an ideal 
scenario, the amount of memory needed for 42 OpenMP threads is the same 
as a single one.

This might explains why you calculation freezes. You are out of memory. 
On your workstation, you should only use the executable "cp2k.ssmp" 
which is the OpenMP version. Then you don't need the mpirun command:

cp2k.ssmp -i inp.inp -o -out.out

To control the number of OpenMP threads, set the env variable: 
OMP_NUM_THREADS, e.g. in bash, export OMP_NUM_THREADS=48

Now, if you need to balance between MPI and OpenMP, you should use the 
executable named cp2k.psmp. Here is such an example:

export OMP_NUM_THREADS=24
mpirun -n 2 cp2k.psmp -i inp.inp -o -out.out

In this example, I am requesting two MPI threads and each of them can 
use up to 24 OpenMP threads.

Hope this clarifies things for you.

Regards,
Pierre

On 20/09/2019 14:09, Nikhil Maroli wrote:
> Dear all,
>
> I have installed all the versions of CP2K in my workstation with 2 x 
> 12 core processor, total thread=48
>
> I wanted to run cp2k in parallel using 42 threads, can anyone share 
> the commands that i can use.
>
> I have tried
>
> mpirun -n 42 cp2k.pop -i inp.inp -o -out.out
>
> After this command there is a rise in memory to 100 % and the whole 
> system freezes. (i have 128GB ram).
>
> Any suggestion will be greatly appreciated,
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-- 
Dr Pierre Cazade, PhD
AD3-023, Bernal Institute,
University of Limerick,
Plassey Park Road,
Castletroy, co. Limerick,
Ireland

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