[Users] TAT/ Slab Error

[Roland Haas]

Hello Karima,

> Here is the error attached I encountered while evolving black holes
> binary. The work-around I guess is to increase the number of
> processes (if I am not wrong), but I am not quite sure how to do
> that. I need some help to get around this issue.
Assuming you use simulation factory you need to pass options to make
sure it creates multiple MPI processes. The auto-detection code tends
to choose a number of threads equal to the the number of cores on your
laptop and and a single MPI rank.

Eg if you have a 4 core laptop then you have to use:

./simfactory/bin/sim submit testrun01 --cores 4 --num-threads 2
--parfile ...

which uses a total of 4 cores and starts 2 threads per MPI rank so that
you end up with 4 / 2 = 2 MPI ranks each of which uses 2 threads.

Similarly on clusters, the basic idea is to set --num-threads so that
there are more than 1 MPI rank started (ie --num-threads is larger than
the value for --cores or --procs [which are synonyms for each other]).

If not using simulation factory you have to manually use mpirun and
OMP_NUM_THREADS. Eg:

export OMP_NUM_THREADS=2

mpirun -np 2 /home/karima/simulations/bbhHr/SIMFACTORY/exe/cactus_sim
-L 3 /home/karima/simulations/bbhHr/output-0000/BBHHigherRes.par

which starts 2 MPI ranks each will use 2 OpenMP threads.

Yours,
Roland

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