MATLAB: Didn’t recognize full workers when using ‘matlabpool’

parallel computingParallel Computing Toolbox

Hi,

I have trouble in connecting to full labs for the parallel computing.

>> matlabpool open
Starting matlabpool using the 'local' profile ... connected to 2 labs.

As you can see above, only two labs could be connected for the parallel computing, but I am using quad-core PC that means four labs have to be connected. Moreover, the strange thing is that four labs was connected when using the Matlab version R2008a (Now I am using Matlab version R2012a).

Would you help me out with that problem?

Thank you.

Seongjun Park

Best Answer

I would venture to guess that you have a machine with hyper-threading. This essentially means that two cores are presented as four. You can read more about it here:

http://en.wikipedia.org/wiki/Hyper-threading

If you wish to open four labs, you can do so by using Kaustubha's suggestion or by changing the NumWorkers property of the local scheduler to have four.

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MATLAB: MatLab R2011a detects 8 physical cores when I only have 4!

This Xeon uses hyper-threading, as shown here:

http://ark.intel.com/products/48501/Intel-Xeon-Processor-X3480-%288M-Cache-3_06-GHz%29

This means, that each core can process two threads at the same time. Therefore it is a good idea to start 8 workers.

MATLAB: Use both multi core CPUs

You need to edit the 'local' parallel profile to set the maximum number of workers to 32. See the doc. Once you've done that, you should be able to issue the following command:

parpool('local', 32)

and launch 32 workers.

Note that if MATLAB by default does not consider hyper-threaded cores, as these tend not to perform well for numerically intensive computations. So, you might well find that running 32 workers is actually slower than running 16, depending on the precise nature of your computation.

Best Answer

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