Disable hyperthreading from within Linux (no access to BIOS)

You can do this at runtime if you want to. I found a nice solution described here: http://www.absolutelytech.com/2011/08/01/how-to-disable-cpu-cores-in-linux/

Step 1: Identify the linux CPUs you want to switch off:

cat /proc/cpuinfo

Look for the CPUs that have the same "core id", you want to switch off one of each pair.

Step 2: Switch off the hyperthreading CPUs (in my case the last four of the total 8 "CPUs" seen by Linux)

echo 0 > /sys/devices/system/cpu/cpu4/online
echo 0 > /sys/devices/system/cpu/cpu5/online
echo 0 > /sys/devices/system/cpu/cpu6/online
echo 0 > /sys/devices/system/cpu/cpu7/online

You could setup yourself a script that you run just after system start.

Newer Kernels provide a Simultaneous Multithreading (SMT) control.

You can check the state of SMT with;

cat /sys/devices/system/cpu/smt/active

Change the state with

echo off > /sys/devices/system/cpu/smt/control

Options are;

• on
• off
• forceoff

We have tested this with Linux Kernel 4.4.0