[PATCH] sched/deadline: Add update_rq_clock() in yield_task_dl()

[PATCH] sched/deadline: Add update_rq_clock() in yield_task_dl()

[Xunlei Pang]

yield_task_dl() calls update_curr_dl() which calls start_dl_timer()
to throttle current task. But yield_task_dl() doesn't update the rq
clock which will cause start_dl_timer() to set the wrong dl_timer
which may be much later than current deadline time.

For instance, in systems with 100HZ tick, if there're few dl-tasks,
then rq clock will mainly depend on the tick to update its value.
If we choose the CONFIG_NO_HZ_FULL_ALL feature, things may get even
worse.

Moreover, there're some statistics in update_curr_dl() also relying
on rq clock, like rq_clock_task().

Thus, in yield_task_dl(), we should add update_rq_clock() before
update_curr_dl().

Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
---
 kernel/sched/deadline.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e5db8c6..5648e62 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -915,7 +915,11 @@ static void yield_task_dl(struct rq *rq)
 		rq->curr->dl.dl_yielded = 1;
 		p->dl.runtime = 0;
 	}
+
+	update_rq_clock(rq);
 	update_curr_dl(rq);
+	/* Will go to schedule(), to avoid another clock update. */
+	rq->skip_clock_update = 1;
 }
 
 #ifdef CONFIG_SMP
-- 
1.9.1

Re: [PATCH] sched/deadline: Add update_rq_clock() in yield_task_dl()

[Xunlei Pang]

Hi Kirill,

I've also sent out this similar patch to yours before,
and I agree with you on this point :-)

But with the latest modification which peter made,
( see: cebde6d681aa45f96111cfcffc1544cf2a0454ff )
I think it would be better to add a skip operation
after update_curr_dl(rq) like below:

---
 kernel/sched/deadline.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e5db8c6..5648e62 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -915,7 +915,11 @@ static void yield_task_dl(struct rq *rq)
                rq->curr->dl.dl_yielded = 1;
                p->dl.runtime = 0;
        }
+
+       update_rq_clock(rq);
        update_curr_dl(rq);
+       /* Will go to schedule(), to avoid another clock update. */
+       rq_clock_skip_update(rq, true);
 }

#ifdef CONFIG_SMP
--
1.9.1

On 19 December 2014 at 00:31, Xunlei Pang <pang.xunlei@linaro.org> wrote:
> yield_task_dl() calls update_curr_dl() which calls start_dl_timer()
> to throttle current task. But yield_task_dl() doesn't update the rq
> clock which will cause start_dl_timer() to set the wrong dl_timer
> which may be much later than current deadline time.
>
> For instance, in systems with 100HZ tick, if there're few dl-tasks,
> then rq clock will mainly depend on the tick to update its value.
> If we choose the CONFIG_NO_HZ_FULL_ALL feature, things may get even
> worse.
>
> Moreover, there're some statistics in update_curr_dl() also relying
> on rq clock, like rq_clock_task().
>
> Thus, in yield_task_dl(), we should add update_rq_clock() before
> update_curr_dl().
>
> Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
> ---
>  kernel/sched/deadline.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index e5db8c6..5648e62 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -915,7 +915,11 @@ static void yield_task_dl(struct rq *rq)
>                 rq->curr->dl.dl_yielded = 1;
>                 p->dl.runtime = 0;
>         }
> +
> +       update_rq_clock(rq);
>         update_curr_dl(rq);
> +       /* Will go to schedule(), to avoid another clock update. */
> +       rq->skip_clock_update = 1;
>  }
>
>  #ifdef CONFIG_SMP
> --
> 1.9.1
>

Re: [PATCH] sched/deadline: Add update_rq_clock() in yield_task_dl()

[Xunlei Pang]

On 4 February 2015 at 21:28, Xunlei Pang <pang.xunlei@linaro.org> wrote:
> Hi Kirill,
>
> I've also sent out this similar patch to yours before,
> and I agree with you on this point :-)
>
> But with the latest modification which peter made,
> ( see: cebde6d681aa45f96111cfcffc1544cf2a0454ff )

My mistake, the commit should be:
9edfbfed3f544a7830d99b341f0c175995a02950 (tip tree)

Thanks,
Xunlei

Re: [PATCH] sched/deadline: Add update_rq_clock() in yield_task_dl()

[Kirill Tkhai]

Hi, Xunlei,

В Ср, 04/02/2015 в 21:28 +0800, Xunlei Pang пишет:
> I've also sent out this similar patch to yours before,
> and I agree with you on this point :-)

I missed your patch, thanks for the pointing to it.

> But with the latest modification which peter made,
> ( see: cebde6d681aa45f96111cfcffc1544cf2a0454ff )
> I think it would be better to add a skip operation
> after update_curr_dl(rq) like below:
> 
> ---
>  kernel/sched/deadline.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index e5db8c6..5648e62 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -915,7 +915,11 @@ static void yield_task_dl(struct rq *rq)
>                 rq->curr->dl.dl_yielded = 1;
>                 p->dl.runtime = 0;
>         }
> +
> +       update_rq_clock(rq);
>         update_curr_dl(rq);
> +       /* Will go to schedule(), to avoid another clock update. */
> +       rq_clock_skip_update(rq, true);
>  }
> 
> #ifdef CONFIG_SMP
> --
> 1.9.1
> 
> On 19 December 2014 at 00:31, Xunlei Pang <pang.xunlei@linaro.org> wrote:
> > yield_task_dl() calls update_curr_dl() which calls start_dl_timer()
> > to throttle current task. But yield_task_dl() doesn't update the rq
> > clock which will cause start_dl_timer() to set the wrong dl_timer
> > which may be much later than current deadline time.
> >
> > For instance, in systems with 100HZ tick, if there're few dl-tasks,
> > then rq clock will mainly depend on the tick to update its value.
> > If we choose the CONFIG_NO_HZ_FULL_ALL feature, things may get even
> > worse.
> >
> > Moreover, there're some statistics in update_curr_dl() also relying
> > on rq clock, like rq_clock_task().
> >
> > Thus, in yield_task_dl(), we should add update_rq_clock() before
> > update_curr_dl().
> >
> > Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
> > ---
> >  kernel/sched/deadline.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index e5db8c6..5648e62 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -915,7 +915,11 @@ static void yield_task_dl(struct rq *rq)
> >                 rq->curr->dl.dl_yielded = 1;
> >                 p->dl.runtime = 0;
> >         }
> > +
> > +       update_rq_clock(rq);
> >         update_curr_dl(rq);
> > +       /* Will go to schedule(), to avoid another clock update. */
> > +       rq->skip_clock_update = 1;
> >  }
> >
> >  #ifdef CONFIG_SMP
> > --
> > 1.9.1
> >

Kirill