[Bug 1885730] Re: Bring back ondemand.service or switch kernel default governor for pstate - pstate now defaults to performance governor

** Also affects: linux (Ubuntu Groovy)
Importance: Undecided
Status: Confirmed

** Also affects: systemd (Ubuntu Groovy)
Importance: Undecided
Status: New

** Tags removed: rls-gg-incoming

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https://bugs.launchpad.net/bugs/1885730

Title:
Bring back ondemand.service or switch kernel default governor for
pstate - pstate now defaults to performance governor

Status in linux package in Ubuntu:
Confirmed
Status in systemd package in Ubuntu:
New
Status in linux source package in Groovy:
Confirmed
Status in systemd source package in Groovy:
New

Bug description:
In a recent merge from Debian we lost ondemand.service, meaning all
CPUs now run in Turbo all the time when idle, which is clearly
suboptimal.

The discussion in bug 1806012 seems misleading, focusing on p-state vs
other drivers, when in fact, the script actually set the default
governor for the pstate driver on platforms that use pstate.
Everything below only looks at systems that use pstate.

pstate has two governors: performance and powerstate. performance runs
CPU at maximum frequency constantly, and powersave can be configured
using various energy profiles energy profiles:

- performance
- balanced performance
- balanced power
- power

It defaults to balanced performance, I think, but I'm not sure.

Whether performance governor is faster than powersave governor is not
even clear.
https://www.phoronix.com/scan.php?page=article&item=linux50-pstate-
cpufreq&num=5 benchmarked them, but did not benchmark the individual
energy profiles.

For a desktop/laptop, the expected behavior is the powersave governor
with balanced_performance on AC and balanced_power on battery.

I don't know about servers or VMs, but the benchmark series seems to
indicate it does not really matter much performance wise.

I think most other distributions configure their kernels to use the
powersave governor by default, whereas we configure it to use the
performance governor and then switch it later in the boot to get the
maximum performance during bootup. It's not clear to me that's
actually useful.

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