Enable hyperthreading (temporarily)

# sysctl hw.smt=1

Disable hyperthreading (temporarily)

# sysctl hw.smt=0

Enable hyperthreading (permanently)

# echo "hw.smt=1" >> /etc/sysctl.conf

Disable hyperthreading (permanently)

# echo "hw.smt=0" >> /etc/sysctl.conf