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Why did spmd create a pool of 12 workers on a cluster with 32 cores?

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Claire Fang
Claire Fang on 16 Jul 2021
Commented: Kojiro Saito on 19 Jul 2021
I am experiencing a problem with running Matlab code with spmd blocks on the cedar cluster on Compute Canada. I asked for 32 cores and 1 node being allocated to me. The system can detect 32 cores, but spmd can generate a pool of only 12 workers.
Can someone explain why? I am attaching both the Matlab file and the output file here.

Accepted Answer

Kojiro Saito
Kojiro Saito on 16 Jul 2021
In Parallel Preferences "Preferred number of workers" is set to 12 by default.
You can change this value to 100 (more than 32) in Preferences menu.
Alternatively, you can specify workers in parpool.
You can add parpool(num) before spmd blocks.
parpool(num)
spmd(num)
...
end
  4 Comments
Kojiro Saito
Kojiro Saito on 19 Jul 2021
Usually, parpool will create a job directory, but in your universities clusters, home directory was set to read-only. I didn't know that, but I'm glad the issue is solved now.

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