Re: Bug in scheduler when using rt_mutex

[Yong Zhang]

On Thu, Jan 20, 2011 at 2:12 PM, Mike Galbraith <efault@xxxxxx> 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. ÂSo 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.

Thanks,
Yong

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