cpu cores and threads

cpu cores and threads

newport_j's picture
newport_j
Tue, 01/24/2012 - 08:44

In the attached graphics files that are shown, the screenshots show that I have seven threads, but I only have four cpu cores as shown in the second graphic screenshot.

My cpu is a four core Xeon, with hyperthreading.I am just unsure as to how that converts four cores to seven threads.

Any help appreciated. Thanks in advance.

Both screenshots are of the same screen, one shows the top of the screen and the other shows the bottom of the screen. They are realy just two views of the same screen.

Newport_j

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jimdempseyatthecove's picture
jimdempseyatthecove
Wed, 01/25/2012 - 20:29

Your second screen shot shows a report listing

"Logical CPU count 4"

This would indicate HyperThreading is disabled.

Your system can have any number of threads (memory permitting) regardless of the number of "Logical CPUs". Usually the standard proceedure of OpenMP, TBB, CilkPlus, etc... is tocreate a thread pool equal to the number of logical CPU's (available to the Process (application)). Some threading models create additional helper threads (e.g. display output, watchdog, etc...). So you could see additional threads in your report. The helper threads will not run any of your application code and should be easily identified by looking at the routines executed by the thread.

HyperThreading is enabled or disabled with a BIOS setting.

Jim Dempsey

Blog: The Parallel Void

www.quickthreadprogramming.com
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iliyapolak's picture
iliyapolak
Wed, 02/13/2013 - 00:32

Your system has four physical cores and if <strong>HT</strong> is enabled you have 8 logical cores(each physical core has two logical cores each with its own set of gp registers and APIC).Number of OS threads can reach hundreds and only as much as 8 can be scheduled to run on your CPU at any moment.

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Sergey Kostrov's picture
Sergey Kostrov
Wed, 02/13/2013 - 06:59

>>...In the attached graphics files that are shown, the screenshots show that I have seven threads...

Sorry, I don't see any screenshots.

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