Messages in this thread | | | Date | Tue, 28 Feb 2017 17:47:53 +0000 | From | Juri Lelli <> | Subject | Re: [PATCH v3] sched/deadline: Change the time to replenish runtime for sleep tasks |
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On 28/02/17 22:09, Byungchul Park wrote: > On Tue, Feb 28, 2017 at 11:35:15AM +0000, Juri Lelli wrote: > > Hi, > > > > On 23/02/17 15:14, Byungchul Park wrote: > > > Let's consider the following example. > > > > > > timeline : o...................o.........o.......o..o > > > ^ ^ ^ ^ ^ > > > | | | | | > > > start | | | | > > > original runtime | | | > > > sleep with (-)runtime | | > > > original deadline | > > > wake up > > > > > > When this task is woken up, a negative runtime should be considered, > > > which means that the task should get penalized when assigning runtime, > > > becasue it already spent more than expected. Current code handles this > > > by replenishing a runtime in hrtimer callback for deadline. But this > > > approach has room for improvement: > > > > > > It will be replenished twice unnecessarily if the task sleeps for > > > long time so that the deadline, assigned in the hrtimer callback, > > > also passed. In other words, one happens in the callback and the > > > other happens in update_dl_entiry() when waking it up. > > > > > > So force to replenish it for sleep tasks when waking it up. > > > > > > Signed-off-by: Byungchul Park <byungchul.park@lge.com> > > > --- > > > kernel/sched/deadline.c | 13 ++++++------- > > > 1 file changed, 6 insertions(+), 7 deletions(-) > > > > > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > > > index 27737f3..cb43ce9 100644 > > > --- a/kernel/sched/deadline.c > > > +++ b/kernel/sched/deadline.c > > > @@ -498,8 +498,9 @@ static void update_dl_entity(struct sched_dl_entity *dl_se, > > > struct dl_rq *dl_rq = dl_rq_of_se(dl_se); > > > struct rq *rq = rq_of_dl_rq(dl_rq); > > > > > > - if (dl_time_before(dl_se->deadline, rq_clock(rq)) || > > > - dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) { > > > + if (dl_time_before(dl_se->deadline, rq_clock(rq))) > > > + replenish_dl_entity(dl_se, pi_se); > > > + else if (dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) { > > > dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline; > > > dl_se->runtime = pi_se->dl_runtime; > > > } > > > @@ -621,13 +622,11 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) > > > * __dequeue_task_dl() > > > * prev->on_rq = 0; > > > * > > > - * We can be both throttled and !queued. Replenish the counter > > > - * but do not enqueue -- wait for our wakeup to do that. > > > + * We can be both throttled and !queued. Wait for our wakeup to > > > + * replenish runtime and enqueue p. > > > */ > > > - if (!task_on_rq_queued(p)) { > > > - replenish_dl_entity(dl_se, dl_se); > > > > Hasn't this patch the same problem we discussed a couple of weeks ago? > > No. This patch solves the problem by calling replenish_dl_entity() when > a dl task is woken up. >
So, if the task was throttled in the "going to sleep" path we set the replenishment timer to fire at your "original deadline" instant of time above. Now, 3 things can happen I guess:
- task wakes up before the replenishment timer ("original deadline") -> it is throttled, so we do nothing
- task wakes up after the replenishment timer -> we replenished it in the timer callback (which considers negative runtime from previous execution) + deadline should be in the future + dl_entity shouldn't overflow + we don't touch its parameters, but we simply enqueue it back on dl_rq
- task wakes up even after the deadline it has got from previous replenishment expired -> we assign to him completely new parameters, but since he didn't use the previous runtime at all, this should be fine I guess
What am I still missing? :)
> The problem was that it cannot consider negative runtime if we replenish > the task when it's woken up. So I made replenish_dl_entity() called even > on wake-up path, instead of simple assignment. > > IMHO, this patch avoids double-replenishing properly, but adds additional > condition on wake-up path to acheive it. To be honest, I don't think it's > worth as I expected. > > Thank you, > Byungchul > > > > > https://marc.info/?l=linux-kernel&m=148699950802995 > > > > Thanks, > > > > - Juri
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