Messages in this thread |  | | | Date | Fri, 21 Jan 2011 21:15:01 +0800 | | From | Yong Zhang <> | | Subject | Re: Bug in scheduler when using rt_mutex |
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On Thu, Jan 20, 2011 at 11:07:27AM +0100, Mike Galbraith wrote: > On Thu, 2011-01-20 at 17:07 +0800, Yong Zhang wrote: > > 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 ;) > > That's ok, we don't and aren't supposed to care what happens while he's > gone. But we do have to make sure that vruntime is sane either when he > leaves, or when he comes back. Seems to me the easiest is clip when he > leaves to cover him having slept a long time before leaving, then coming > back on us as a runner. If he comes back as a sleeper, he'll be clipped > again anyway, so all is well.
OK, fair enough.
> > sched_fork() should probably zero child's vruntime too, so non-fair > children can't enter fair_class with some bogus lag they never had.
Yeah, So I think Peter's new patch is taking care of all the issue now.
Thanks, Yong
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