Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 6 Dec 2017 10:39:52 +0100 | Subject | Re: [PATCH v3 4/6] sched/rt: fast switch to maximum frequency when RT tasks are scheduled |
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Hi Patrick,
On 30 November 2017 at 12:47, Patrick Bellasi <patrick.bellasi@arm.com> wrote: > Currently schedutil updates are triggered for the RT class using a single > call place, which is part of the rt::update_curr_rt() used in: > > - dequeue_task_rt: > but it does not make sense to set the schedutil's SCHED_CPUFREQ_RT in > case the next task should not be an RT one > > - put_prev_task_rt: > likewise, we set the SCHED_CPUFREQ_RT flag without knowing if required > by the next task > > - pick_next_task_rt: > likewise, the schedutil's SCHED_CPUFREQ_RT is set in case the prev task > was RT, while we don't yet know if the next will be RT > > - task_tick_rt: > that's the only really useful call, which can ramp up the frequency in > case a RT task started its execution without a chance to order a > frequency switch (e.g. because of the schedutil ratelimit) > > Apart from the last call in task_tick_rt, the others are at least useless. > Thus, although being a simple solution, not all the call sites of that > update_curr_rt() are interesting to trigger a frequency switch as well as > some of the most interesting points are not covered by that call. > For example, a task set to RT has to wait the next tick to get the > frequency boost. > > This patch fixes these issues by placing explicitly the schedutils > update calls in the only sensible places, which are: > - when an RT task wakes up and it's enqueued in a CPU > - when we actually pick a RT task for execution > - at each tick time > - when a task is set to be RT > > Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Cc: linux-kernel@vger.kernel.org > Cc: linux-pm@vger.kernel.org > > --- > Changes from v2: > - rebased on v4.15-rc1 > - use cpufreq_update_util() instead of cpufreq_update_this_cpu() > > Change-Id: I3794615819270fe175cb118eef3f7edd61f602ba > --- > kernel/sched/rt.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 4056c19ca3f0..6984032598a6 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -959,9 +959,6 @@ static void update_curr_rt(struct rq *rq) > if (unlikely((s64)delta_exec <= 0)) > return; > > - /* Kick cpufreq (see the comment in kernel/sched/sched.h). */ > - cpufreq_update_util(rq, SCHED_CPUFREQ_RT); > - > schedstat_set(curr->se.statistics.exec_max, > max(curr->se.statistics.exec_max, delta_exec)); > > @@ -1327,6 +1324,9 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags) > > if (!task_current(rq, p) && p->nr_cpus_allowed > 1) > enqueue_pushable_task(rq, p); > + > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */ > + cpufreq_update_util(rq, SCHED_CPUFREQ_RT); > } > > static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags) > @@ -1564,6 +1564,9 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) > > p = _pick_next_task_rt(rq); > > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
p is null when there is no rt task to pick. You should test this condition before calling cpufreq_update_util
> + cpufreq_update_util(rq, SCHED_CPUFREQ_RT); > + > /* The running task is never eligible for pushing */ > dequeue_pushable_task(rq, p); > > @@ -2282,6 +2285,9 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued) > { > struct sched_rt_entity *rt_se = &p->rt; > > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */ > + cpufreq_update_util(rq, SCHED_CPUFREQ_RT); > + > update_curr_rt(rq); > > watchdog(rq, p); > @@ -2317,6 +2323,9 @@ static void set_curr_task_rt(struct rq *rq) > > p->se.exec_start = rq_clock_task(rq); > > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */ > + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
Is this change linked to the "- when a task is set to be RT" in the commit message ?
I can't see a situation where this is call without the previous one. AFAICT, enqueue_task_rt will be called before each call to this function
> + > /* The running task is never eligible for pushing */ > dequeue_pushable_task(rq, p); > } > -- > 2.14.1 >
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