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Old 01-31-2013, 08:33 AM   #1
Registered: Feb 2011
Location: UK
Distribution: RHEL 5 & 6, Ubuntu 10
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Reduced CPU cores to 4, but Linux says there are still 8

We have a test server running RHEL 5.8. The platform is a HP BL460c blade server with 2x 4-core Xeon CPUs.

The server was set up with all 8 cores enabled, but we now wish to reduce the number of cores to 4 on this test system, in order to simulate a lower powered server.

I have reduced the number of active cores to 4 in the machine's BIOS, and it reports that there are 4 cores total available on boot (previously it reported a total of 8).

But when Linux comes up, it still shows 8 CPUs (in /proc/cpuinfo, /var/log/messages, dmidecode, top, etc.).

I'm looking for some help as to how I can have Linux correctly identify the number of cores that the machine it is running on has?

(NB. we chose to limit the cores in the BIOS, rather than as an OS boot option.)

Thanks for looking!
Old 01-31-2013, 09:32 AM   #2
Registered: Aug 2012
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Its due to hyper-threading, it enables each CPU to handle two threads simultaneosly.
Old 01-31-2013, 11:26 AM   #3
Registered: Feb 2011
Location: UK
Distribution: RHEL 5 & 6, Ubuntu 10
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Thanks - I was getting there...

On looking back through syslog files, Linux was listing 16 "CPU"s when there were 8 cores configured, so reducing the cores to 4 with 2 threads per core gives 8 "CPU"s.
Old 01-31-2013, 11:33 AM   #4
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If you choose, you can disable hyperthreading in the BIOS.

Do you want to "simulate a lower powered server" that has hyperthreading enabled, or one that doesn't?


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