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

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Claire Fang 2021-7-16

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https://ww2.mathworks.cn/matlabcentral/answers/879683-why-did-spmd-create-a-pool-of-12-workers-on-a-cluster-with-32-cores

评论： Kojiro Saito 2021-7-19

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.

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Kojiro Saito 2021-7-16

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https://ww2.mathworks.cn/matlabcentral/answers/879683-why-did-spmd-create-a-pool-of-12-workers-on-a-cluster-with-32-cores#answer_747948

在 MATLAB Online 中打开

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

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Claire Fang 2021-7-19

在 MATLAB Online 中打开

@Kojiro Saito, you are right. It is related. Apparently I needed to prepare a .matlab folder on the server. Instructions are shown on https://docs.computecanada.ca/wiki/MATLAB. Below is the code:

[name@cluster ~]$ cd $HOME
[name@cluster ~]$ if [ -d ".matlab" ]; then
  mv .matlab scratch/
else
  mkdir -p scratch/.matlab
fi && ln -sn scratch/.matlab .matlab 

Once I did that, everything worked. Thanks!

Kojiro Saito 2021-7-19

@Claire Fang

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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