[Bug 1806012] Re: set-cpufreq: 'powersave' governor configuration sanity on ubuntu server

[Trent Lloyd]

Something I was not previously aware of that informs this a bit more, is
that in some BIOS modes (apparently HP uses this extensively, unsure
about Dell and others) you get a "Collaborative Power Control" mode,
which sets the scaling_driver to pcc-cpufreq (as opposed to cpufreq) and
is some weird hybrid of OS+BIOS defined behavior.

In the case of these collaborative modes, the exact behavior is probably
wildly different based on what the BIOS is doing and likely would
explain why we get weird and inconsistent performance behavior. Unclear
to me if such BIOS modes will still use intel_pstate or not.. something
I'd have to look into. Or whether it's specific to pre-pstate.

Some more information about collaborative mode in this bug:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1447763

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https://bugs.launchpad.net/bugs/1806012

Title:
  set-cpufreq: 'powersave' governor configuration sanity on ubuntu
  server

Status in systemd package in Ubuntu:
  In Progress
Status in systemd source package in Xenial:
  In Progress
Status in systemd source package in Bionic:
  In Progress
Status in systemd source package in Cosmic:
  In Progress
Status in systemd source package in Disco:
  In Progress

Bug description:
  Whilst debugging 'slow instance performance' on a Ubuntu Bionic based
  cloud, I observed that the default cpu governor configuration was set
  to 'powersave'; toggling this to 'performance' (while in not anyway a
  particularly green thing todo) resulted in the instance slowness
  disappearing and the cloud performance being as expected (based on a
  prior version of the deploy on Ubuntu Xenial).

  AFAICT Xenial does the same thing albeit in a slight different way,
  but we definitely did not see the same performance laggy-ness under a
  Xenial based cloud.

  Raising against systemd (as this package sets the governor to
  'powersave') - I feel that the switch to 'performance' although
  appropriate then obscures what might be a performance/behavioural
  difference in the underlying kernel when a machine is under load.

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: systemd 237-3ubuntu10.9
  ProcVersionSignature: Ubuntu 4.15.0-39.42-generic 4.15.18
  Uname: Linux 4.15.0-39-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.5
  Architecture: amd64
  Date: Fri Nov 30 10:05:46 2018
  Lsusb:
   Bus 002 Device 002: ID 8087:8002 Intel Corp. 
   Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
   Bus 001 Device 003: ID 413c:a001 Dell Computer Corp. Hub
   Bus 001 Device 002: ID 8087:800a Intel Corp. 
   Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
  MachineType: Dell Inc. PowerEdge R630
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=C.UTF-8
   SHELL=/bin/bash
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.15.0-39-generic root=UUID=a361a524-47eb-46c3-8a04-e5eaa65188c9 ro hugepages=103117 iommu=pt intel_iommu=on
  SourcePackage: systemd
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 11/08/2016
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: 2.3.4
  dmi.board.name: 02C2CP
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A03
  dmi.chassis.type: 23
  dmi.chassis.vendor: Dell Inc.
  dmi.modalias: dmi:bvnDellInc.:bvr2.3.4:bd11/08/2016:svnDellInc.:pnPowerEdgeR630:pvr:rvnDellInc.:rn02C2CP:rvrA03:cvnDellInc.:ct23:cvr:
  dmi.product.name: PowerEdge R630
  dmi.sys.vendor: Dell Inc.

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