Ubuntu
linux package

context switching on 3.11 kernel costing CPU and power

Bug #1233681 reported by Colin Ian King on 2013-10-01

This bug affects 3 people

Affects		Status	Importance	Assigned to	Milestone
	linux (Ubuntu)	Fix Released	Medium	Colin Ian King
	Saucy	Fix Released	Medium	Colin Ian King

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.

CVE References

2013-2147

Revision history for this message

Colin Ian King (colin-king) wrote on 2013-10-01:

LibreOffice file containing test results - old config vs fixed config Edit (39.3 KiB, application/vnd.oasis.opendocument.spreadsheet)

Changed in linux (Ubuntu):
importance:	Undecided → Medium
status:	New → In Progress
assignee:	nobody → Colin King (colin-king)

Tim Gardner (timg-tpi) on 2013-10-01

Changed in linux (Ubuntu Saucy):
status:	In Progress → Fix Committed

Revision history for this message

Launchpad Janitor (janitor) wrote on 2013-10-02:

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 <email address hidden> Tue, 01 Oct 2013 07:24:27 -0600