Messages in this thread | | | Date | Mon, 26 Dec 2011 16:42:57 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH]sched: stop hrtick timer if running task is switching from fair scheduling class to another |
| |
On 12/23, Kirill Tkhai wrote: > > [PATCH]sched: stop hrtick timer if running task is switching from fair > scheduling class to another > > We have to stop hrtick timer to avoid excess interrupt. Not-fair tasks > are not interested in fair's hrtick. RT class uses its own fixed > timeslice (in case of RR), which doesn't depend on current value of hrtick > timer.
Well. I shouldn't try to comment this patch, I do not really understand this code.
But since nobody else replies...
> @@ -5271,6 +5271,13 @@ static void switched_from_fair(struct rq *rq, > struct task_struct *p) > place_entity(cfs_rq, se, 0); > se->vruntime -= cfs_rq->min_vruntime; > } > + > + /* > + * Other scheduling classes are not interested in fair's hrtick timer. > + */ > + if (task_current(rq, p) && sched_feat(HRTICK)) > + hrtick_clear(rq); > + > }
May be... but in this case, perhaps instead we should teach dequeue_task_fair() or put_prev_task_fair() to do this. Then we can probably remove __schedule()->hrtick_clear().
I simply can't understand the current hrtick logic. For example, why dequeue_task_fair() does hrtick_update() ? OK, probably because "nr_running < sched_nr_latency" can become true. But at least this doesn't make sense to me when p == rq->curr, say, __schedule() path.
Hmm. In any case, how it is possible to do hrtick_start() with rq->lock held? hrtimer_restart() may want to wakeup_softirqd().
Peter, Ingo, does this code really work? SCHED_FEAT(HRTICK) == 0 by default, and afaics you can't change it without CONFIG_SCHED_DEBUG.
Confused...
Oleg.
| |