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

[Dan Streetman]

> I would suggest switching back to powersave/ondemand either with a new
service or the kernel config.

re: new service, the existing package cpufrequtils (and related package
cpufreqd) provides a configurable service to manage governor settings
(and other related settings).  The old ondemand service was not
configurable at all and caused quite a bit of unexpected problems, as
well as 'battling' (overriding) the cpufrequtils service when it was
installed.

> Having a dedicated service could be confusing for people who try to
change the kernel settings.

indeed, it was, especially when there were multiple services to (try to)
control the settings that conflicted with each other.

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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:
  Invalid
Status in linux source package in Groovy:
  Confirmed
Status in systemd source package in Groovy:
  Invalid

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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