parpool problems: fewer running processes than workers

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Gregory Johnson
Gregory Johnson on 23 Jul 2016
Commented: Thomas Ibbotson on 27 Jul 2016
I'm currently trying to debug a problem with my parallel computing toolbox setup. I'm running MATLAB 2016a in a CentOS virtual machine, and have assigned the guest machine 22 cores. My host machine has 88 cores.
I have started a parpool with 22 workers, and if I terminate my job and look at the pool properties, it does, in fact, indicate that I am running 22 workers:
p = gcp('nocreate')
p =
Pool with properties:
Connected: true
NumWorkers: 22
Cluster: local
AttachedFiles: {}
IdleTimeout: 30 minute(s) (30 minutes remaining)
SpmdEnabled: true
Here is the problem: If I look at 'htop' in the guest, only 12 worker processes will be running at a time, as shown in this screenshot:
I can confirm that my guest vm IS utilizing 22 different cores on the host machine, but will only fully utilize 12 of those cores at a time.
Any suggestions?
  1 Comment
Thomas Ibbotson
Thomas Ibbotson on 27 Jul 2016
I think we'd need to see what code you are running on the pool to have any chance of figuring this out. Can you provide that?
You clearly have plenty of workers, in fact I count 39 in your screenshot, so you should be able to use them all. The fact you're only getting 12 is a little suspicious because that's the default number of workers Parallel Computing Toolbox uses for pools.

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