kernel-packages team mailing list archive

[Doug Smythies <1188647@xxxxxxxxxxxxxxxxxx>]

For the decision to re-enable the intel pstate driver by default or not,
the suggestion is to be cautious. The driver keeps changing in rather
fundamental ways, such that one can never be sure how it is going to
perform. I will attach two graphs to (hopefully) help make my point.

The first graph demonstrates a dramatic difference in CPU frequency
scaling response as a function of load between kernel 3.12 and 3.15RC2
at a fixed idle (sleep) / work frequency.

The second graph (to be posted in a moment) demonstrates a dramatic
difference in CPU scaling frequency as a function of idle (sleep) /work
frequency at a fixed load.

Don't get me wrong here, as I am a proponent of the intel_pstate driver,
but I am concerned about how its response to stimulus keeps changing.


** Attachment added: "CPU 7 frequency vs load. Turbo on. Kernels 3.15RC2 and 3.12"
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1188647/+attachment/4097698/+files/k315rc2_k312_load_sweep_200.png

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https://bugs.launchpad.net/bugs/1188647

Title:
  Please change intel_pstate default to disable

Status in “linux” package in Ubuntu:
  Fix Released

Bug description:
  3.9 introduced a new default governor on SandyBridge CPUs called
  INTEL_PSTATE which, when built in and enabled (the default), removes
  all other governors (like our usual default, ondemand). 3.10 extended
  this to Ivybridge generation CPUs.

  In theory, this isn't an awful thing, as the new Intel pstate governor
  should be higher performance and give better power savings.  In
  theory.

  In practice, it drives my CPUs to max frequency nearly constantly,
  spins my fans like mad and, somehow, does all of this while also
  eating enough CPU time in kernel threads to make my machine choppy,
  unresponsive, and unable to do simple things like play videos when I
  get off work.

  Therefore, I propose that we, for now, toggle intel_pstate to disable
  by default (I am using intel_pstate=disable on my command line right
  now, with great success), so it's still built in, and people can play
  with it, but it's off by default.

  ProblemType: Bug
  DistroRelease: Ubuntu 13.10
  Package: linux-image-3.9.0-4-generic 3.9.0-4.9
  ProcVersionSignature: Ubuntu 3.9.0-4.9-generic 3.9.4
  Uname: Linux 3.9.0-4-generic x86_64
  ApportVersion: 2.10.2-0ubuntu1
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  adconrad   2574 F.... pulseaudio
  CurrentDmesg:
   [   30.633035] init: plymouth-stop pre-start process (2079) terminated with status 1
   [   36.086916] br0: port 1(eth0) entered forwarding state
  Date: Fri Jun  7 08:48:56 2013
  HibernationDevice: RESUME=UUID=73040efa-baec-458a-8307-3bca07b26c3c
  InstallationDate: Installed on 2012-12-09 (179 days ago)
  InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Alpha amd64 (20121209)
  MachineType: LENOVO 4173LPB
  MarkForUpload: True
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.9.0-4-generic root=UUID=2222aad5-ef31-4428-973f-71740fc7cb6a ro intel_pstate=disable quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.9.0-4-generic N/A
   linux-backports-modules-3.9.0-4-generic  N/A
   linux-firmware                           1.109
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 09/13/2012
  dmi.bios.vendor: LENOVO
  dmi.bios.version: 8CET55WW (1.35 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 4173LPB
  dmi.board.vendor: LENOVO
  dmi.board.version: Not Available
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Not Available
  dmi.modalias: dmi:bvnLENOVO:bvr8CET55WW(1.35):bd09/13/2012:svnLENOVO:pn4173LPB:pvrThinkPadT420s:rvnLENOVO:rn4173LPB:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 4173LPB
  dmi.product.version: ThinkPad T420s
  dmi.sys.vendor: LENOVO

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