Public bug reported: 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. ** Affects: linux (Ubuntu) Importance: Medium Assignee: Colin King (colin-king) Status: In Progress ** Attachment added: "LibreOffice file containing test results - old config vs fixed config" https://bugs.launchpad.net/bugs/1233681/+attachment/3853414/+files/pm-config-fixes.ods ** Changed in: linux (Ubuntu) Importance: Undecided => Medium ** Changed in: linux (Ubuntu) Status: New => In Progress ** Changed in: linux (Ubuntu) Assignee: (unassigned) => Colin King (colin-king) -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1233681 Title: context switching on 3.11 kernel costing CPU and power Status in “linux” package in Ubuntu: In Progress 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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1233681/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
