Messages in this thread | | | Date | Wed, 19 Jan 2011 10:38:57 +0800 | Subject | Re: Bug in scheduler when using rt_mutex | From | Yong Zhang <> |
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On Tue, Jan 18, 2011 at 9:35 PM, Peter Zijlstra <peterz@infradead.org> wrote: > Subject: sched: Fix switch_to_fair() > From: Peter Zijlstra <a.p.zijlstra@chello.nl> > Date: Mon Jan 17 17:03:27 CET 2011 > > When a task is placed back into fair_sched_class, we must update its > placement, since we don't know how long its been gone, hence its > vruntime is stale and cannot be trusted. > > There is also a case where it was moved from fair_sched_class when it > was in a blocked state and moved back while it is running, this causes > an imbalance between DEQUEUE_SLEEP/DEQUEUE_WAKEUP for the fair class > and leaves vruntime way out there (due to the min_vruntime > adjustment). > > Also update sysrq-n to call the ->switch_{to,from} methods. > > Reported-by: Onkalo Samu <samu.p.onkalo@nokia.com> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > --- > kernel/sched.c | 4 ++++ > kernel/sched_fair.c | 16 ++++++++++++++++ > 2 files changed, 20 insertions(+) > > Index: linux-2.6/kernel/sched_fair.c > =================================================================== > --- linux-2.6.orig/kernel/sched_fair.c > +++ linux-2.6/kernel/sched_fair.c > @@ -4075,6 +4075,22 @@ static void prio_changed_fair(struct rq > static void switched_to_fair(struct rq *rq, struct task_struct *p, > int running) > { > + struct sched_entity *se = &p->se; > + struct cfs_rq *cfs_rq = cfs_rq_of(se); > + > + if (se->on_rq && cfs_rq->curr != se)
(cfs_rq->curr != se) equals to (!running), no?
> + __dequeue_entity(cfs_rq, se); > + > + /* > + * se->vruntime can be completely out there, there is no telling > + * how long this task was !fair and on what CPU if any it became > + * !fair. Therefore, reset it to a known, reasonable value. > + */ > + se->vruntime = cfs_rq->min_vruntime;
But this is not fair for !SLEEP task. You know se->vruntime -= cfs_rq->min_vruntime for !SLEEP task, then after it go through sched_fair-->sched_rt-->sched_fair by some means, current cfs_rq->min_vruntime is added back.
But here se is putted before where it should be. Is this what we want?
Thanks, Yong
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