parallel computing: matlab only uses half the cores available. Help?

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Luis Hernandez 2016-11-2

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编辑： Dylan Gomes 2023-3-6

Hello,

I have a machine with 40 cores and I'm trying to use them all for a job. I have set the preferred number of workers to 40 in the Preferences, but I can see that matlab is only using 20 workers. Any suggestions about how to fix this? Thanks a lot

-L

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Adam 2016-11-2

Does it have 40 actual cores or is it 20 with hyper-threading? I know next to nothing about hyper-threading, but I know my machine has 28 physical cores, but 56 show up in my task manager due to hyper threading. Matlab only uses the 28 though.

Mujahid Sultan 2017-8-13

编辑：Mujahid Sultan 2017-8-14

I have the same issue, "nproc" shows 56 where as Matlab only uses 28 cpus, features('nucores') shows 28 cores. Interestingly the map-reduce function of Matlab uses all 56 cores and returns only results for 28. I am loosing half of my computations somewhere.

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Kojiro Saito 2016-11-2

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On MATLAB,

Go to Parallel Menu -> Manage Cluster Profiles
Edit your cluster profile (name is 'local')
Input 40 (the number of your cores) in "NumWorkers" column and click "Done"

Thanks

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Luis Hernandez 2016-11-2

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I'm afraid I already did what Kojiro suggested- it didn't work and that is why I'm asking on this forum.

@Adam: The machine has 40 actual cores.

thanks again.

-Luis

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Kojiro Saito 2016-11-7

@Luis, could you provide me the version of your MATLAB?

Also, if you can figure out the difference between your settings, please let us know.

Thanks,

Dylan Gomes 2023-3-6

编辑：Dylan Gomes 2023-3-6

在 MATLAB Online 中打开

I thought I was having the same issue with MATLAB R2021a, but it turned out that I only actually have 6 physical cores, when I thought I had 12.

>> feature('numCores')
% 
% MATLAB detected: 6 physical cores.
% MATLAB detected: 12 logical cores.
% MATLAB was assigned: 12 logical cores by the OS.
% MATLAB is using: 6 logical cores.
% MATLAB is not using all logical cores because hyper-threading is enabled.