Bug#489223: kernel: niced processes get half of the CPU (problem with group fair scheduling)
Package: kernel
Severity: normal
Hi,
here is a scenario to illustrate the problem:
- run low priority processes with a 19 nice value (for example
distributed-net aka dnetc) under the identity of a specific user
(daemon)
- run a normal priority process under the identity of a another user
(for example burnP6 from the cpuburn package)
Traditional and expected Unix behavior is to give dnetc a small share of
the CPU and burnP6 should have a large share of the CPU. However here
is the CPU distribution according to "top" on a dual core system:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
27870 daemon 39 19 704 428 336 R 100 0.0 1:01.24 dnetc
28653 daemon 39 19 704 204 112 R 50 0.0 0:56.02 dnetc
29615 bonnaud 20 0 96 16 8 R 50 0.0 0:08.64 burnP6
[...]
According to
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/188226
this can be fixed by changing the kernel configuration. Here is what is
used in Debian:
$ grep GROUP_SCHED /boot/config-2.6.25-2-686
CONFIG_GROUP_SCHED=y
CONFIG_FAIR_GROUP_SCHED=y
# CONFIG_RT_GROUP_SCHED is not set
# CONFIG_CGROUP_SCHED is not set
and here is what is used in Ubuntu:
$ grep GROUP_SCHED /boot/config-2.6.24-19-generic
CONFIG_FAIR_CGROUP_SCHED=y
CONFIG_FAIR_GROUP_SCHED=y
-- System Information:
Debian Release: lenny/sid
APT prefers unstable
APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: i386 (i686)
Kernel: Linux 2.6.25-2-686 (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash
--
Laurent Bonnaud.
http://www.lis.inpg.fr/pages_perso/bonnaud/
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