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 Linux on Dell systems FAQ-O-Matic : Supported Dell systems :
Why does /proc/cpuinfo report twice as many CPUs as I have? |
| On a newly installed linux system (PowerEdge 2650 with 2 2GHz CPUs) the following problem occured: Not 2 but 4 CPUs are reported (dmesg, /proc/cpuinfo, top), but it should be only 2 (also the BIOS reports 2 CPUs)!
The 2 2.4GHz CPUs are being recognized as 2 logical CPUs per processor. This is due to hyper-threading in the new P4 Xeon processors. For more info take a look at this: http://www.intel.com/technology/hyperthread/intro_nexgen/ You can turn off the hyperthreading at the kernel level by either recompiling and/or entering "noht" on the kernel command line. The corollary is true as well--to enable hyperthreading in the kernel either compile it in and/or enter "ht" on the kernel command line.
On most BIOSs you can also disable hyperthreading via the BIOS Setup (F2) screen immediately after power-on.
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