kernel-packages team mailing list archive
-
kernel-packages team
-
Mailing list archive
-
Message #18949
[Bug 1233681] Re: context switching on 3.11 kernel costing CPU and power
** Changed in: linux (Ubuntu Saucy)
Status: In Progress => Fix Committed
--
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:
Fix Committed
Status in “linux” source package in Saucy:
Fix Committed
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
References