Detecting Hyper Threading

(Note: Valid for RHEL family 4, 5, and 6. NOT valid for RHEL family 3.)

Dag explains:

Even though /proc/cpuinfo shows you all the logical CPUs (processor field) in the system, the siblings field holds the number of logical CPUs for the physical CPU this entry belongs to (including both the cores and the hyper-threaded LCPUs).

In other words, if you see: processor : 7 physical id : 9 siblings : 4 cpu cores : 2

It means that LCPU #7 (the eight logical CPU in your system) is one of the 4 logical CPUs on the physical CPU that has 2 cores. So yes, hyper-threading is enabled.

If the number of cpu cores is the same as the number of siblings, hyper-threading is disabled.

So:

# egrep 'siblings|cpu cores' /proc/cpuinfo | sort | uniq
cpu cores       : 10
siblings        : 10

And:

# egrep 'siblings|cpu cores' /proc/cpuinfo | sort | uniq
cpu cores       : 1
siblings        : 2