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[Jason Gerard DeRose <jason@xxxxxxxxxxxx>]

Public bug reported:

The intel pstate driver is currently quite broken on on Skylake
hardware.

The symptom is that the pstate driver can scale the frequency up, but
wont then scale it back down. So as soon as you hit a decent amount of
CPU load, you get stuck fluctuating in the turbo frequency ranges, never
even dropping as low as the base clock frequency. Obviously this has
very negative consequences for battery life.

Commit 74da56ce5c6715630aed3ccc0fcb86a9210c1a56 fixes this upstream,
which is included in 4.3rc2:

https://git.kernel.org/cgit/linux/kernel/git/next/linux-
next.git/commit/?id=74da56ce5c6715630aed3ccc0fcb86a9210c1a56

I built a custom Ubuntu kernel with this commit and tested it on a
laptop with a Skylake i7-6700 CPU. As measured by powerstat, this commit
dropped the idle power consumption by 11 watts (from 34 to 23 watts,
screen backlight was off during the test).

I also tested this custom kernel on Haswell and Ivy Bridge hardware to
make sure it didn't introduce any behaviour changes in the pstate driver
on older hardware. As far as I can tell, on this older hardware pstate
is behaving exactly the same with and without this commit.

Thanks!

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: skylake wily

** Attachment added: "intel_pstate-fix-PCT_TO_HWP-macro.patch"
   https://bugs.launchpad.net/bugs/1499040/+attachment/4472580/+files/intel_pstate-fix-PCT_TO_HWP-macro.patch

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https://bugs.launchpad.net/bugs/1499040

Title:
  Wily: Skylake: intel_pstate: fix PCT_TO_HWP macro

Status in linux package in Ubuntu:
  New

Bug description:
  The intel pstate driver is currently quite broken on on Skylake
  hardware.

  The symptom is that the pstate driver can scale the frequency up, but
  wont then scale it back down. So as soon as you hit a decent amount of
  CPU load, you get stuck fluctuating in the turbo frequency ranges,
  never even dropping as low as the base clock frequency. Obviously this
  has very negative consequences for battery life.

  Commit 74da56ce5c6715630aed3ccc0fcb86a9210c1a56 fixes this upstream,
  which is included in 4.3rc2:

  https://git.kernel.org/cgit/linux/kernel/git/next/linux-
  next.git/commit/?id=74da56ce5c6715630aed3ccc0fcb86a9210c1a56

  I built a custom Ubuntu kernel with this commit and tested it on a
  laptop with a Skylake i7-6700 CPU. As measured by powerstat, this
  commit dropped the idle power consumption by 11 watts (from 34 to 23
  watts, screen backlight was off during the test).

  I also tested this custom kernel on Haswell and Ivy Bridge hardware to
  make sure it didn't introduce any behaviour changes in the pstate
  driver on older hardware. As far as I can tell, on this older hardware
  pstate is behaving exactly the same with and without this commit.

  Thanks!

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