Thursday, November 17, 2005

Disabling Hyper-Threading

The use of Hyper-Threading for server applications is questionable, especially if the number of I/O requests is high. To determine the cost or the potential performance improvements it makes sense to disable the Hyper-threading (from known on abbreviated with HT) support. The are two ways to disable HT:
  • Disable Hyper-Threading in the kernel
  • Disable Hyper-threading by the BIOS
Intel recommends to disable Hyper-Threading in the BIOS as it is more cleanly to disable at that point. To disable it in the BIOS look for a description logical CPU (this how it is called for Dell servers) or something similar.

The other option is to specify the noht switch in the kernel line of the grub configuration file. Unfortunately this doesn't work with Redhat AS 4.

To check if HT is really disabled check the file /proc/cpuinfo. This file should only report the physical CPU's.

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