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[Launchpad Bug Tracker <1233681@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package linux - 3.11.0-11.17

---------------
linux (3.11.0-11.17) saucy; urgency=low

  [ Andy Whitcroft ]

  * [Packaging] tools -- only build common tools package in master
  * SAUCE: tools -- report when tool is not available
    - LP: #1233376
  * [Packaging] tools -- common tools must carry all possible tools
    - LP: #1233376

  [ Colin Ian King ]

  * [Config] Fix power and performance regression
    - LP: #1233681

  [ Colin Watson ]

  * [Config] Clean up various udeb Provides

  [ Tim Gardner ]

  * rebase to v3.11.3
  * Release tracker
    - LP: #1233808

  [ Upstream Kernel Changes ]

  * ALSA: hda - Add CS4208 codec support for MacBook 6,1 and 6,2
    - LP: #1233623
  * ALSA: hda - Add fixup for MacBook Air 6,1 and 6,2 with CS4208 codec
    - LP: #1233623
  * NVMe: Remove "process_cq did something" message
    - LP: #1233686
  * Drivers: hv: balloon: Initialize the transaction ID just before sending the packet
    - LP: #1233466
  * cciss: fix info leak in cciss_ioctl32_passthru()
    - LP: #1188355
    - CVE-2013-2147
  * cpqarray: fix info leak in ida_locked_ioctl()
    - LP: #1188355
    - CVE-2013-2147
  * Drivers: hv: util: Fix a bug in version negotiation code for util services
    - LP: #1233433
 -- Tim Gardner <tim.gardner@xxxxxxxxxxxxx>   Tue, 01 Oct 2013 07:24:27 -0600

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

** CVE added: http://www.cve.mitre.org/cgi-
bin/cvename.cgi?name=2013-2147

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https://bugs.launchpad.net/bugs/1233681

Title:
  context switching on 3.11 kernel costing CPU and power

Status in “linux” package in Ubuntu:
  Fix Released
Status in “linux” source package in Saucy:
  Fix Released

Bug description:
  Heavy context switching is consuming a lot of extra power with the
  current saucy kernel.    Context switching intensive tasks are
  consuming much longer to complete than on 3.8 raring kernels, for
  example:

  dd if=/dev/zero | cat | cat | dd of=/dev/null

  See http://reports.qa.ubuntu.com/power/hardware/arch/amd64/

  The reason is that CONFIG_CONTEXT_TRACKING_FORCE is turned on because
  CONFIG_NO_HZ_FULL is enabled and the former config option adds a lot
  of overhead to context switching.

  See attached LibreOffice spreadsheet with tests with the original
  config and the new fixed config.  Endurance tests take less time to
  run to completion and the overall coulombs used is less with
  CONTEXT_TRACKING_FORCE and NO_HZ_FULL disabled, so this is an overall
  win.   Some tests, such as the dd copy take way less time to complete,
  showing massive overhead of CONTEXT_TRACKING_FORCE.

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