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[Bruno Chareyre <question690973@xxxxxxxxxxxxxxxxxxxxx>]

Question #690973 on Yade changed:
https://answers.launchpad.net/yade/+question/690973

Bruno Chareyre proposed the following answer:
> I understand you suggestion to get the optimal price of cores. But now
for me, to get the fastest speed of the simulation is the aim.

Yes. That's exactly my point. It could be that the fastest is -j1, or
that it is just equal.

Here is some bad news: if you write an ordinary python program and you
assign more than one openMP thread to it, the change of execution time
will be null. You can try on your server by running a minimal program,
just try this in the command line:

:~$ export OMP_NUM_THREADS=1
:~$ time python3 -c "for k in range(int(1e7)): a=k**0.124" 
real    0m2.240s
user    0m2.190s
sys     0m0.009s

Then:
:~$ export OMP_NUM_THREADS=96
:~$ time python3 -c "for k in range(int(1e7)): a=k**0.124" 
real    0m2.190s
user    0m2.181s
sys     0m0.008s

That's how programming works in many cases.  The variable
OMP_NUM_THREADS is even not used when python runs. It is the same for
your PyRunners. The fact that yade is parallel doesn't make *your*
program parallel.

Here is the good news:
If you have to train your algorithm on many realizations then you can train 96 cases simultaneously  (assuming RAM is enough). Which will be *much* faster.
You can, either, hire colleagues to have more hands clicking the open/close for 96 planks (will need many keyboards/mices with long cables for social distancing), or (safer) do it with hard numbers as Jan suggested.

If really you have no choice but running one single script at a time,
then you need to re-think what your simulation script is doing - with a
good idea of where/how time is spent.

B.

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