Messages in this thread | | | Date | Wed, 11 Jan 2017 17:05:42 +0000 | From | Juri Lelli <> | Subject | Re: [RFC v4 2/6] sched/deadline: improve the tracking of active utilization |
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Hi,
On 30/12/16 12:33, Luca Abeni wrote: > From: Luca Abeni <luca.abeni@unitn.it> > > This patch implements a more theoretically sound algorithm for > tracking active utilization: instead of decreasing it when a > task blocks, use a timer (the "inactive timer", named after the > "Inactive" task state of the GRUB algorithm) to decrease the > active utilization at the so called "0-lag time". > > Signed-off-by: Luca Abeni <luca.abeni@unitn.it> > ---
[...]
> +static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer) > +{ > + struct sched_dl_entity *dl_se = container_of(timer, > + struct sched_dl_entity, > + inactive_timer); > + struct task_struct *p = dl_task_of(dl_se); > + struct rq_flags rf; > + struct rq *rq; > + > + rq = task_rq_lock(p, &rf); > + > + if (!dl_task(p) || p->state == TASK_DEAD) { > + if (p->state == TASK_DEAD && dl_se->dl_non_contending) > + sub_running_bw(&p->dl, dl_rq_of_se(&p->dl)); > + > + __dl_clear_params(p); > + > + goto unlock; > + } > + if (dl_se->dl_non_contending == 0) > + goto unlock; > + > + sched_clock_tick(); > + update_rq_clock(rq); > + > + sub_running_bw(dl_se, &rq->dl); > + dl_se->dl_non_contending = 0; > +unlock: > + task_rq_unlock(rq, p, &rf); > + put_task_struct(p); > + > + return HRTIMER_NORESTART; > +} > +
[...]
> static void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline) > @@ -934,7 +1014,28 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se, > if (flags & ENQUEUE_WAKEUP) { > struct dl_rq *dl_rq = dl_rq_of_se(dl_se); > > - add_running_bw(dl_se, dl_rq); > + if (dl_se->dl_non_contending) { > + /* > + * If the timer handler is currently running and the > + * timer cannot be cancelled, inactive_task_timer() > + * will see that dl_not_contending is not set, and > + * will do nothing, so we are still safe.
Here and below: the timer callback will actually put_task_struct() (see above) if dl_not_contending is not set; that's why we don't need to do that if try_to_cancel returned -1 (or 0). Saying "will do nothing" is a bit misleading, IMHO.
> + */ > + if (hrtimer_try_to_cancel(&dl_se->inactive_timer) == 1) > + put_task_struct(dl_task_of(dl_se)); > + WARN_ON(dl_task_of(dl_se)->nr_cpus_allowed > 1); > + dl_se->dl_non_contending = 0; > + } else {
[...]
> @@ -1097,6 +1198,22 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags) > } > rcu_read_unlock(); > > + rq = task_rq(p); > + raw_spin_lock(&rq->lock); > + if (p->dl.dl_non_contending) { > + sub_running_bw(&p->dl, &rq->dl); > + p->dl.dl_non_contending = 0; > + /* > + * If the timer handler is currently running and the > + * timer cannot be cancelled, inactive_task_timer() > + * will see that dl_not_contending is not set, and > + * will do nothing, so we are still safe. > + */ > + if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1) > + put_task_struct(p); > + } > + raw_spin_unlock(&rq->lock); > + > out: > return cpu; > }
We already raised the issue about having to lock the rq in select_task_rq_dl() while reviewing the previous version; did you have any thinking about possible solutions? Maybe simply bail out (need to see how frequent this is however) or use an inner lock?
Best,
- Juri
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