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SubjectRe: [BUG] sched: fair group's bug
on 2009-1-8 9:30 Miao Xie wrote:
> I tested fair group scheduler on my hyper-threading x86_64 box(2 CPU * 2 HT)
> and found the deviation of the groups' CPU usage was larger than 2.6.26
> when *offline* a CPU or do hotplug frequently. It is less than 1% On 2.6.26,but
> On current kernel, it is often greater than 4%, even than 10% by accident.
>

This patch fixed the following problems. But the regression above still exists.

commit 0a582440ff546e2c6610d1acec325e91b4efd313
Author: Mike Galbraith <efault@gmx.de>
Date: Fri Jan 2 12:16:42 2009 +0100

sched: fix sched_slice()

Impact: fix bad-interactivity buglet

Fix sched_slice() to emit a sane result whether a task is currently
enqueued or not.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Tested-by: Jayson King <dev@jaysonking.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

>
> Besides that, We found other problems by the attached program.
> 1. some tasks are hungry in the fair group.
> Steps to reproduce:
> # mkdir /dev/cpuctl
> # mount -t cgroup -o cpu,noprefix xxx /dev/cpuctl
> # ./cpuctl -g 1 -v
> --------------------
> 1th Check Result:
> Group Shares Actual(%) Expect(%)
> 0 1024 100.00 100.00
> Each task's usage:
> Task in Group 0:
> Task Usage(%)
> 5395 0.000000
> 5396 0.000000
> 5397 0.000000
> 5398 16.677785
> 5399 16.677785
> 5400 16.744496
> 5401 16.611074
> 5402 33.288859
>
> 2. some groups broke the limit of the fair group and get more CPU time When
> the groups is hiberarchy. Such as:
> top group
> |
> group 1
> / \
> task1 group 2
> |
> task 2
> Steps to reproduce:
> # mkdir /dev/cpuctl
> # mount -t cgroup -o cpu,noprefix xxx /dev/cpuctl
> # ./cpuctl -H
> -------------------------
> Group Shares Actual(%) Expect(%)
> 0 1024 60.17 88.89
> 1 1024 39.83 11.11
>


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