With the default Ubuntu 13.04 sysctl settings and boot parameters, positively niced tasks are very clearly given a larger share of CPU time than they ought to be. The update-apt-xapian-index process, for instance, runs at niceness +19; but it still slows my Celeron M520 laptop to a crawl. Likewise for other positively niced tasks.
If, on the other hand, I boot with the 'noautogroup' kernel parameter (which sets kernel.sched_autogroup_enabled to 0), responsiveness is much better when running CPU heavy tasks at positive niceness.
In both cases, processes are reported by top and ps as running at the correct niceness; it appears that the nice level is ignored silently.
Autogrouping is supposed to provide better responsiveness under some loads, but I believe that breaking nice settings is too high a price. I think it would be a good idea to turn off kernel.sched_autogroup_enabled, until this behavior is fixed upstream.
By the way, an important note: modifying the sched_autogroup_enabled sysctl on a running system will usually cause a kernel panic. Autogrouping needs to be turned off using 'noautogroup' as a boot parameter; if you try it using sysctl.conf you will get a nice kernel panic on boot.
---
ApportVersion: 2.9.2-0ubuntu8.3
Architecture: i386
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: proteus 1939 F.... pulseaudio
CurrentDmesg:
[ 23.536912] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 70.086188] nr_pdflush_threads exported in /proc is scheduled for removal
[ 70.086403] sysctl: The scan_unevictable_pages sysctl/node-interface has been disabled for lack of a legitimate use case. If you have one, please send an email to <email address hidden>.
[ 186.829290] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
DistroRelease: Ubuntu 13.04
HibernationDevice: RESUME=UUID=ef3fd95f-4429-4c81-8aa1-30d57be5d48c
InstallationDate: Installed on 2013-09-01 (0 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release i386 (20130424)
MachineType: Acer, inc. Aspire 3680
MarkForUpload: True
Package: linux (not installed)
PccardctlIdent:
Socket 0:
no product info available
PccardctlStatus:
Socket 0:
no card
ProcEnviron:
TERM=xterm
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.8.0-29-generic root=UUID=779c7e91-1548-4942-b184-7b10797b86b8 ro quiet splash autogroup vt.handoff=7
ProcVersionSignature: Ubuntu 3.8.0-29.42-generic 3.8.13.5
RelatedPackageVersions:
linux-restricted-modules-3.8.0-29-generic N/A
linux-backports-modules-3.8.0-29-generic N/A
linux-firmware 1.106
Tags: raring
Uname: Linux 3.8.0-29-generic i686
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
dmi.bios.date: 10/27/06
dmi.bios.vendor: Acer
dmi.bios.version: v1.3216
dmi.board.name: Prespa1
dmi.board.vendor: Acer, Inc.
dmi.board.version: Not Applicable
dmi.chassis.type: 1
dmi.chassis.vendor: Acer, Inc.
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAcer:bvrv1.3216:bd10/27/06:svnAcer,inc.:pnAspire3680:pvrNotApplicable:rvnAcer,Inc.:rnPrespa1:rvrNotApplicable:cvnAcer,Inc.:ct1:cvrN/A:
dmi.product.name: Aspire 3680
dmi.product.version: Not Applicable
dmi.sys.vendor: Acer, inc.
This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:
apport-collect 1219548
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the Ubuntu Kernel Team.