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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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