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I have a simple stress test that has a configurable number of threads based on the server it's running on. On one Windows machine with 16 cores I'm able to start the process which in turn launches 16 threads and keeps all cores maxxed out for the duration of the test.

On another Windows machine with 16 cores I run the test but it only uses 8 of the 16 available i.e it's using one CPU and not the other.

I'm aware this is more of a Windows config question than a Java question as I've shown the test itself behaves as expected on one machine and not another.

Using Task Manager I can see the system has 16 cores but something is preventing access to the other 8.

Is there a setting that is preventing a single process using all the cores?

If StackOverflow isn't the correct home for this question, please suggest another Stack* where I should move it.

Update One

On the problematic machine I was previously attempting to run 1 process with 16 threads. If I run two processes with 8 threads each I am able to consume 100% of the cores.

imrichardcole
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  • Is it just Java that is unable to use the other 8 cores, or can no program use them? – Joni Feb 27 '16 at 08:47
  • @Joni I'm trying to find something I can run to answer that question. Will update question shortly. – imrichardcole Feb 27 '16 at 08:52
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    There is nothing in Java which allows you to limit the number of cores it can use, you couldn't do what you suggest in Java alone if you wanted to. It must be configured at the OS level. – Peter Lawrey Feb 27 '16 at 10:44
  • @PeterLawrey fully agree. As stated in the question, this isn't a Java issue. I included the fact it was a Java test as people would ask what I was running and also how I could be confident of how many threads I was launching. – imrichardcole Feb 27 '16 at 10:48

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This turned out to be the same issue that's posted here:

Unable to use more than one processor group for my threads in a C# app

Which in turn links to an HP advisory here:

http://h20566.www2.hpe.com/hpsc/doc/public/display?sp4ts.oid=5379860&docId=emr_na-c04650594&docLocale=en_US

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