Messages in this thread Patch in this message | | | Subject | Re: Bug in scheduler when using rt_mutex | From | Peter Zijlstra <> | Date | Fri, 21 Jan 2011 12:08:56 +0100 |
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On Thu, 2011-01-20 at 11:07 +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. > > 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.
Something like so?
Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c +++ linux-2.6/kernel/sched.c @@ -2624,6 +2624,8 @@ void sched_fork(struct task_struct *p, i if (!rt_prio(p->prio)) p->sched_class = &fair_sched_class; + else + p->se.vruntime = 0; if (p->sched_class->task_fork) p->sched_class->task_fork(p); Index: linux-2.6/kernel/sched_fair.c =================================================================== --- linux-2.6.orig/kernel/sched_fair.c +++ linux-2.6/kernel/sched_fair.c @@ -4086,8 +4086,14 @@ static void switched_from_fair(struct rq * have normalized the vruntime, if it was !on_rq, then only when * the task is sleeping will it still have non-normalized vruntime. */ - if (!se->on_rq && p->state != TASK_RUNNING) + if (!se->on_rq && p->state != TASK_RUNNING) { + /* + * Fix up our vruntime so that the current sleep doesn't + * cause 'unlimited' sleep bonus. + */ + place_entity(cfs_rq, se, 0); se->vruntime -= cfs_rq->min_vruntime; + } } /*
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