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    SubjectRe: Bug in scheduler when using rt_mutex
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    On Thu, Jan 20, 2011 at 4:37 PM, Mike Galbraith <efault@gmx.de> wrote:
    > On Thu, 2011-01-20 at 15:06 +0800, Yong Zhang wrote:
    >> On Thu, Jan 20, 2011 at 2:12 PM, Mike Galbraith <efault@gmx.de> wrote:
    >> > If the task returns as a sleeper, place entity() will be called when it
    >> > is awakened, so it's sleep credit will be clipped as usual.  So vruntime
    >> > can be much less than min_vruntime at class exit time, and it doesn't
    >> > matter, clipping on wakeup after re-entry takes care of it.. if that's
    >> > what you were thinking about.
    >>
    >> For a sleep task which stay in sched_fair before it's waked:
    >> try_to_wake_up()
    >>   ttwu_activate()
    >>     activate_task()
    >>       enqueue_task_fair()
    >>         enqueue_entity()
    >>           place_entity()        <== clip vruntime
    >>
    >> For a sleep task which promote to sched_rt when it's sleep:
    >> rt_mutex_setprio()
    >>   check_class_changed()
    >>     switch_from_fair()       <== vruntime -= min_vruntime
    >>       try_to_wake_up()
    >>         ...run then stay on rq
    >>         rt_mutex_setprio()
    >>           enqueue_task_fair()     <==vruntime += min_vruntime
    >>
    >> The difference is that in the second case, place_entity() is not
    >> called, but wrt sched_fair, the task is a WAKEUP task.
    >> Then we place this task in sched_fair before where it should be.
    >
    > D'oh.  You're right, he needs to be clipped before he leaves.

    Exactly we should clip it when it comes back, because it still could
    sleep for some time after it leaves ;)

    Thanks,
    Yong

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