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[Launchpad Bug Tracker <1499040@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package linux - 4.2.0-12.14

---------------
linux (4.2.0-12.14) wily; urgency=low

  [ Tim Gardner ]

  * Release Tracking Bug
    - LP: #1499712

  [ Ben Pope ]

  * SAUCE: drivers/net/ethernet/atheros/alx: Add Killer E2400 device ID
    - LP: #1498633

  [ Knuth Posern ]

  * SAUCE: thunderbolt: Allow loading of module on recent Apple MacBooks
    with thunderbolt 2 controller
    - LP: #1497321

  [ Laurent Dufour ]

  * SAUCE: powerpc/hvsi: Fix endianness issues in the HVSI driver
    - LP: #1499357

  [ Upstream Kernel Changes ]

  * x86/hyperv: Mark the Hyper-V TSC as unstable
    - LP: #1498206
  * intel_pstate: fix PCT_TO_HWP macro
    - LP: #1499040
  * perf/x86/intel/rapl: Add support for Knights Landing (KNL)
    - LP: #1461370
  * drm/i915: Add audio pin sense / ELD callback
    - LP: #1398277
  * drm/i915: Call audio pin/ELD notify function
    - LP: #1398277
  * ALSA: hda - allow codecs to access the i915 pin/ELD callback
    - LP: #1398277
  * ALSA: hda - Wake the codec up on pin/ELD notify events
    - LP: #1398277
  * drm/i915: Add locks around audio component bind/unbind
    - LP: #1398277
  * drm/i915: Drop port_mst_index parameter from pin/eld callback
    - LP: #1398277

 -- Tim Gardner <tim.gardner@xxxxxxxxxxxxx>  Thu, 24 Sep 2015 09:19:23
-0600

** Changed in: linux (Ubuntu Wily)
       Status: Fix Committed => Fix Released

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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:
  Fix Released
Status in linux source package in Wily:
  Fix Released

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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