Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running

From: Rafael J. Wysocki
Date: Tue Apr 19 2016 - 20:29:49 EST


On Monday, April 18, 2016 01:51:24 PM Wanpeng Li wrote:
> Sometimes update_curr() is called w/o tasks actually running, it is
> captured by:
> u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start;
> We should not trigger cpufreq update in this case for rt/deadline
> classes, and this patch fix it.
>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

The signed-off-by tag should agree with the From: header. One way to achieve
that is to add an extra From: line at the start of the changelog.

That said, this looks like a good catch that should go into 4.6 to me.

Peter, what do you think?

> ---
> kernel/sched/deadline.c | 8 ++++----
> kernel/sched/rt.c | 8 ++++----
> 2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index affd97e..8f9b5af 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -717,10 +717,6 @@ static void update_curr_dl(struct rq *rq)
> if (!dl_task(curr) || !on_dl_rq(dl_se))
> return;
>
> - /* Kick cpufreq (see the comment in linux/cpufreq.h). */
> - if (cpu_of(rq) == smp_processor_id())
> - cpufreq_trigger_update(rq_clock(rq));
> -
> /*
> * Consumed budget is computed considering the time as
> * observed by schedulable tasks (excluding time spent
> @@ -736,6 +732,10 @@ static void update_curr_dl(struct rq *rq)
> return;
> }
>
> + /* kick cpufreq (see the comment in linux/cpufreq.h). */
> + if (cpu_of(rq) == smp_processor_id())
> + cpufreq_trigger_update(rq_clock(rq));
> +
> schedstat_set(curr->se.statistics.exec_max,
> max(curr->se.statistics.exec_max, delta_exec));
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index c41ea7a..19e1306 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -953,14 +953,14 @@ static void update_curr_rt(struct rq *rq)
> if (curr->sched_class != &rt_sched_class)
> return;
>
> - /* Kick cpufreq (see the comment in linux/cpufreq.h). */
> - if (cpu_of(rq) == smp_processor_id())
> - cpufreq_trigger_update(rq_clock(rq));
> -
> delta_exec = rq_clock_task(rq) - curr->se.exec_start;
> if (unlikely((s64)delta_exec <= 0))
> return;
>
> + /* Kick cpufreq (see the comment in linux/cpufreq.h). */
> + if (cpu_of(rq) == smp_processor_id())
> + cpufreq_trigger_update(rq_clock(rq));
> +
> schedstat_set(curr->se.statistics.exec_max,
> max(curr->se.statistics.exec_max, delta_exec));
>
>