Multi-threaded batch job on SGE

I would like to run a Julia script which makes use of multi-threading on a Sun Grid Engine cluster. I can reserve 2 cores, load Julia, and run the script with 4 threads by submitting

#$ -pe smp 2
module load julia/1.7.1
julia --threads 4 xyz.jl > ...

The script runs correctly except that it takes it about 4 times as long to finish the calculation as using just a single thread, so it looks like Julia doesn’t actually distribute the treads over all of the available cores and so doesn’t run them in parallel. I don’t have this problem when running the script on my PC instead of on the cluster. What am I doing wrong?

Hi, I think it usually is faster to limit the number of threads to the number of physical cores. By 2 cores do you mean physical or logical cores?

If you are working with 2 logical cores on a single physical processor, then I think the slowdown you observe makes sense.