Parallel Toolbox sets a max of 1 workers on new cluster in R2020b

Both R2020a and R2020b exhibit this behavior on our new cluster where you start matlab then do >>parpool(10).

It responds "You requested a minimum of 10 workers, but the cluster "local" has the

NumWorkers property set to allow a maximum of 1 workers"

There are 94 cores available to jobs on each node.

In the Environment / Parallel / Create and Manage Clusters, NumWorkers is left blank which is the default setting of number of cores. The difference with this cluster is that Matlab is built on a VM and not on a compute node, like the older one

Our older cluster responds with:

Connected to the parallel pool (number of workers: 10).

ans =

ProcessPool with properties:

Connected: true

NumWorkers: 10

Cluster: local

AttachedFiles: {}

AutoAddClientPath: true

IdleTimeout: 30 minutes (30 minutes remaining)

SpmdEnabled: true

[Raymond Norris]

What does

feature numcores

return?

[Christopher S Reidy]

MATLAB is selecting SOFTWARE OPENGL rendering.

< M A T L A B (R) >

Copyright 1984-2020 The MathWorks, Inc.

R2020b Update 1 (9.9.0.1495850) 64-bit (glnxa64)

September 30, 2020

To get started, type doc.

For product information, visit www.mathworks.com.

Using 1 thread(s) on compute node.

>> feature numcores

MATLAB detected: 96 physical cores.

MATLAB detected: 96 logical cores.

MATLAB was assigned: 1 logical cores by the OS.

MATLAB is using: 1 logical cores.

MATLAB is not using all logical cores because Operating System restricted the number of cores to: 1.

ans =

1

[Raymond Norris]

Some more follow-up. Are you running MATLAB

• on Windows, Linux, or Mac?
• via a scheduler (e.g. Slurm)?
• from within cgroups?
• on a Superdome Flex Server?

[Walter Roberson]

The output showd glnxa64 so it must be Linux.

I would suggest checking the environment variables to see if they are telling matlab to use only one core.

[Christopher S Reidy]

Hi Raymond

It is built on a Centos 7 VM and run on centos 7 compute nodes. The VM has 8 cores and the compute nodes have 94 cores available to Slurm with cgroups

Chris

[Christopher S Reidy]

Hi Walter

Yes - good clue - glnxa64. That is the question - which environment variable? We havent found one yet

Thanks, Chris

Answer 1

[Aghamarsh Varanasi]

 Hi,

The issue could be with the other applications running in parallel with MATLAB or the system configurations. Hence this cannot be reproduced at our end. I suggest you contact MathWorks support to resolve the issue.

www.mathworks.com/support/contact_us

[Christopher S Reidy]

Yes - done.

Thanks