High CPU usage of CFS
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
linux (Ubuntu) |
Confirmed
|
Low
|
Unassigned |
Bug Description
It appears that there is an issue with the Completely Fair Scheduler (CFS) not intereacting well with sleep commands. I have written up a test program to help demonstrate the issue and it can be found at:
www.github.
The test outputs wall time (CPU clock), user time, and system time, but usually only the wall time and user time outputs are meaningful because the system time is so small and usually within the standard deviation for all tests.
I have also attached the results from running this test on an HP Pavilion dm4 and I believe that the gap at the low number of threads is caused by either the processor going into a power saving state because of the sleeping and/or a poor interaction with HyperThreading (scheduling the 2 threads on logical cores rather than separate physical cores).
Because of this, I then ran 4 instances of:
schedtool -a <CPU#> -e nice -19 yes > /dev/null
so that all of the cores would be kept busy during the sleeping and this had an unexpected effect of causing the wall time to increase significantly. I am not sure what the cause of the wall time increase is, but it does help the user time plot display the gap between the sleep methods and the none sleep methods that I believe is a symptom/display of the unexpectedly high CPU usage when the process should be sleeping.
ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: linux-image-
ProcVersionSign
Uname: Linux 3.2.0-31-generic x86_64
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
ApportVersion: 2.0.1-0ubuntu13
Architecture: amd64
ArecordDevices:
**** List of CAPTURE Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: STAC92xx Analog [STAC92xx Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/
Card0.Amixer.info:
Card hw:0 'PCH'/'HDA Intel PCH at 0xc0800000 irq 50'
Mixer name : 'Intel CougarPoint HDMI'
Components : 'HDA:111d76e0,
Controls : 22
Simple ctrls : 10
Date: Fri Sep 28 20:57:35 2012
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
MachineType: Hewlett-Packard HP Pavilion dm4 Notebook PC
ProcEnviron:
TERM=xterm
PATH=(custom, no user)
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=
RelatedPackageV
linux-
linux-
linux-firmware 1.79.1
SourcePackage: linux
StagingDrivers: rts_pstor mei
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 01/17/2012
dmi.bios.vendor: Hewlett-Packard
dmi.bios.version: F.08
dmi.board.
dmi.board.name: 1793
dmi.board.vendor: Hewlett-Packard
dmi.board.version: 41.1C
dmi.chassis.
dmi.chassis.type: 10
dmi.chassis.vendor: Hewlett-Packard
dmi.chassis.
dmi.modalias: dmi:bvnHewlett-
dmi.product.name: HP Pavilion dm4 Notebook PC
dmi.product.
dmi.sys.vendor: Hewlett-Packard
Changed in linux (Ubuntu): | |
status: | New → Confirmed |
Changed in linux (Ubuntu): | |
importance: | Medium → Low |
status: | Incomplete → Confirmed |
Would it be possible for you to test the latest upstream kernel? Refer to https:/ /wiki.ubuntu. com/KernelMainl ineBuilds . Please test the latest v3.6 kernel[0] (Not a kernel in the daily directory) and install both the linux-image and linux-image-extra .deb packages.
Once you've tested the upstream kernel, please remove the 'needs- upstream- testing' tag. Please only remove that one tag and leave the other tags. This can be done by clicking on the yellow pencil icon next to the tag located at the bottom of the bug description and deleting the 'needs- upstream- testing' text.
If this bug is fixed in the mainline kernel, please add the following tag 'kernel- fixed-upstream' .
If the mainline kernel does not fix this bug, please add the tag: 'kernel- bug-exists- upstream' .
If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel- unable- to-test- upstream' .
Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".
Thanks in advance.
[0] http:// kernel. ubuntu. com/~kernel- ppa/mainline/ v3.6-quantal/