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



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