Disable "ondemand" CPU scaling daemon

Ubuntu prior to 18.04

Instead of disabling execution of the /etc/init.d/ondemand (as suggested by George) script you should use the this command

sudo update-rc.d ondemand disable

To make the init system not start the script, this is the recognized way of doing it! Disabling the exec permission (sudo chmod -x /etc/init.d/ondemand) might be overwritten if the package is updated.

Ubuntu 18.04+

Ubuntu relocated this script to ondemand.service which execute /lib/systemd/set-cpufreq; use this command to disable the service

~$ sudo systemctl disable ondemand
Removed /etc/systemd/system/multi-user.target.wants/ondemand.service.

Frequency scaling isn't static. As soon as there is work to do, the CPU hops into action, P states boost up, and everything flies.

It's enabled because it's widely seen as a good thing. Saves you energy (good for your wallet and the environment). Keeps heat down (so important in a server room). And it's pretty unnoticeable.

Moreover on modern Intel chips, if you have scaling on you can use "turbo boost" where one core will run at higher-than-stock speeds for a time. This is very useful for spikes of single-threaded work. Without scaling enabled, you don't get this.

Set all CPUs to performance governor:

for GOVERNOR in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; \
do \
    echo "performance" | sudo tee $GOVERNOR; \
done

All supported governors by Linux kernel:

• performance Run the CPU at the maximum frequency.
• powersave Run the CPU at the minimum frequency.
• userspace Run the CPU at user specified frequencies.
• ondemand Scales the frequency dynamically according to current load. Jumps to the highest frequency and then possibly back off as the idle time increases.
• conservative Scales the frequency dynamically according to current load. Scales the frequency more gradually than ondemand.
• schedutil Scheduler-driven CPU frequency selection

See https://www.kernel.org/doc/Documentation/cpu-freq/governors.txt