[PATCH v2] sched/rt: fix call to cpufreq_update_util

[PATCH v2] sched/rt: fix call to cpufreq_update_util

[Vincent Guittot]

With commit 8f111bc357aa ("cpufreq/schedutil: Rewrite CPUFREQ_RT support")
schedutil governor uses rq->rt.rt_nr_running to detect whether a RT task is
currently running on the CPU and to set frequency to max if necessary.
cpufreq_update_util() is called in enqueue/dequeue_top_rt_rq() but
rq->rt.rt_nr_running as not been updated yet when dequeue_top_rt_rq() is
called so schedutil still considers that a RT task is running when the
last task is dequeued. The update of rq->rt.rt_nr_running happens later
in dequeue_rt_stack()

Fixes: 8f111bc357aa ('cpufreq/schedutil: Rewrite CPUFREQ_RT support')
Cc: <stable@vger.kernel.org> # v4.16+
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
- v2:
  - remove blank line

 kernel/sched/rt.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7aef6b4..a9f1119 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1000,9 +1000,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
 
 	sub_nr_running(rq, rt_rq->rt_nr_running);
 	rt_rq->rt_queued = 0;
-
-	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq, 0);
 }
 
 static void
@@ -1288,6 +1285,9 @@ static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
 		if (on_rt_rq(rt_se))
 			__dequeue_rt_entity(rt_se, flags);
 	}
+
+	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
+	cpufreq_update_util(rq_of_rt_rq(rt_rq_of_se(back)), 0);
 }
 
 static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
-- 
2.7.4

Re: [PATCH v2] sched/rt: fix call to cpufreq_update_util

[Peter Zijlstra]

On Thu, May 17, 2018 at 09:16:43AM +0200, Vincent Guittot wrote:
> With commit
>
>  8f111bc357aa ("cpufreq/schedutil: Rewrite CPUFREQ_RT support")
>
> schedutil governor uses rq->rt.rt_nr_running to detect whether a RT task is
> currently running on the CPU and to set frequency to max if necessary.
>
> cpufreq_update_util() is called in enqueue/dequeue_top_rt_rq() but
> rq->rt.rt_nr_running as not been updated yet when dequeue_top_rt_rq() is
> called so schedutil still considers that a RT task is running when the
> last task is dequeued. The update of rq->rt.rt_nr_running happens later
> in dequeue_rt_stack()
> 
> Fixes: 8f111bc357aa ('cpufreq/schedutil: Rewrite CPUFREQ_RT support')
> Cc: <stable@vger.kernel.org> # v4.16+
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> - v2:
>   - remove blank line
> 
>  kernel/sched/rt.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 7aef6b4..a9f1119 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1000,9 +1000,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
>  
>  	sub_nr_running(rq, rt_rq->rt_nr_running);
>  	rt_rq->rt_queued = 0;
> -
> -	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> -	cpufreq_update_util(rq, 0);
>  }
>  
>  static void
> @@ -1288,6 +1285,9 @@ static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
>  		if (on_rt_rq(rt_se))
>  			__dequeue_rt_entity(rt_se, flags);
>  	}
> +
> +	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> +	cpufreq_update_util(rq_of_rt_rq(rt_rq_of_se(back)), 0);
>  }

Hurm.. I think this is also wrong. See how dequeue_rt_stack() is also
called from the enqueue path. Also, nothing calls cpufreq_update_util()
on the throttle path now.

And talking about throttle; I think we wanted to check rt_queued in that
case.

How about the below?

---
 kernel/sched/cpufreq_schedutil.c |  2 +-
 kernel/sched/rt.c                | 24 ++++++++++++++----------
 kernel/sched/sched.h             |  5 +++++
 3 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index e13df951aca7..1751f9630e49 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -185,7 +185,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
 	struct rq *rq = cpu_rq(sg_cpu->cpu);
 	unsigned long util;
 
-	if (rq->rt.rt_nr_running) {
+	if (rt_rq_is_runnable(&rq->rt)) {
 		util = sg_cpu->max;
 	} else {
 		util = sg_cpu->util_dl;
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7aef6b4e885a..a1108a7da777 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -979,8 +979,14 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			if (sched_rt_runtime_exceeded(rt_rq))
+			if (sched_rt_runtime_exceeded(rt_rq)) {
+				struct rq *rq = rq_of_rt_rq(rt_rq);
+
+				if (&rq->rt == rt_rq)
+					cpufreq_update_util(rq, 0);
+
 				resched_curr(rq);
+			}
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
 		}
 	}
@@ -1000,9 +1006,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
 
 	sub_nr_running(rq, rt_rq->rt_nr_running);
 	rt_rq->rt_queued = 0;
-
-	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq, 0);
 }
 
 static void
@@ -1019,9 +1022,6 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
 
 	add_nr_running(rq, rt_rq->rt_nr_running);
 	rt_rq->rt_queued = 1;
-
-	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq, 0);
 }
 
 #if defined CONFIG_SMP
@@ -1330,6 +1330,8 @@ 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);
+
+	cpufreq_update_util(rq, 0);
 }
 
 static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
@@ -1340,6 +1342,8 @@ static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
 	dequeue_rt_entity(rt_se, flags);
 
 	dequeue_pushable_task(rq, p);
+
+	cpufreq_update_util(rq, 0);
 }
 
 /*
@@ -1533,6 +1537,9 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 	struct task_struct *p;
 	struct rt_rq *rt_rq = &rq->rt;
 
+	if (!rt_rq->rt_queued)
+		return NULL;
+
 	if (need_pull_rt_task(rq, prev)) {
 		/*
 		 * This is OK, because current is on_cpu, which avoids it being
@@ -1560,9 +1567,6 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 	if (prev->sched_class == &rt_sched_class)
 		update_curr_rt(rq);
 
-	if (!rt_rq->rt_queued)
-		return NULL;
-
 	put_prev_task(rq, prev);
 
 	p = _pick_next_task_rt(rq);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c9895d35c5f7..bec7f2eecaf3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -609,6 +609,11 @@ struct rt_rq {
 #endif
 };
 
+static inline bool rt_rq_is_runnable(struct rt_rq *rt_rq)
+{
+	return rq_rq->rt_queued && rt_rq->rt_nr_running;
+}
+
 /* Deadline class' related fields in a runqueue */
 struct dl_rq {
 	/* runqueue is an rbtree, ordered by deadline */

Re: [PATCH v2] sched/rt: fix call to cpufreq_update_util

[Peter Zijlstra]

On Thu, May 17, 2018 at 11:05:30AM +0200, Peter Zijlstra wrote:
> Hurm.. I think this is also wrong. See how dequeue_rt_stack() is also
> called from the enqueue path. Also, nothing calls cpufreq_update_util()
> on the throttle path now.
> 
> And talking about throttle; I think we wanted to check rt_queued in that
> case.

Bah, clearly you also want to update on unthrottle.. but I think there's
more buggered wrt throtteling.

Re: [PATCH v2] sched/rt: fix call to cpufreq_update_util

[Vincent Guittot]

Le Thursday 17 May 2018 à 11:32:06 (+0200), Peter Zijlstra a écrit :
> On Thu, May 17, 2018 at 11:05:30AM +0200, Peter Zijlstra wrote:
> > Hurm.. I think this is also wrong. See how dequeue_rt_stack() is also
> > called from the enqueue path. Also, nothing calls cpufreq_update_util()
> > on the throttle path now.

Yes I missed the point that rt_entities were dequeued then re-enqueued when
a task was either enqueued or dequeued.

That's also means that enqueue_top_rt_rq() is always called when a task is
enqueued or dequeued and also when groups are throttled or unthrottled
In fact, the only point where it's not called, is when root rt_rq is
throttled. So I have prepared the patch below which call cpufreq_update util
in enqueue_top_rt_rq() and also when we throttle the root rt_rq.
According to the tests I have done , it seems to work for enqueue/dequeue and
throttle/unthrottle use cases.

I have re-used your rt_rq_is_runnable() which takes into account rt_queued

---
 kernel/sched/cpufreq_schedutil.c |  2 +-
 kernel/sched/rt.c                | 16 ++++++++++------
 kernel/sched/sched.h             |  5 +++++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index e13df95..1751f96 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -185,7 +185,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
 	struct rq *rq = cpu_rq(sg_cpu->cpu);
 	unsigned long util;
 
-	if (rq->rt.rt_nr_running) {
+	if (rt_rq_is_runnable(&rq->rt)) {
 		util = sg_cpu->max;
 	} else {
 		util = sg_cpu->util_dl;
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7aef6b4..d6b9517 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -508,8 +508,11 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
 
 	rt_se = rt_rq->tg->rt_se[cpu];
 
-	if (!rt_se)
+	if (!rt_se) {
 		dequeue_top_rt_rq(rt_rq);
+		/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
+		cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
+	}
 	else if (on_rt_rq(rt_se))
 		dequeue_rt_entity(rt_se, 0);
 }
@@ -1001,8 +1004,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
 	sub_nr_running(rq, rt_rq->rt_nr_running);
 	rt_rq->rt_queued = 0;
 
-	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq, 0);
 }
 
 static void
@@ -1014,11 +1015,14 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
 
 	if (rt_rq->rt_queued)
 		return;
-	if (rt_rq_throttled(rt_rq) || !rt_rq->rt_nr_running)
+
+	if (rt_rq_throttled(rt_rq))
 		return;
 
-	add_nr_running(rq, rt_rq->rt_nr_running);
-	rt_rq->rt_queued = 1;
+	if (rt_rq->rt_nr_running) {
+		add_nr_running(rq, rt_rq->rt_nr_running);
+		rt_rq->rt_queued = 1;
+	}
 
 	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
 	cpufreq_update_util(rq, 0);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c9895d3..bbebcfe 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -609,6 +609,11 @@ struct rt_rq {
 #endif
 };
 
+static inline bool rt_rq_is_runnable(struct rt_rq *rt_rq)
+{
+	return rt_rq->rt_queued && rt_rq->rt_nr_running;
+}
+
 /* Deadline class' related fields in a runqueue */
 struct dl_rq {
 	/* runqueue is an rbtree, ordered by deadline */
-- 
2.7.4





> > 
> > And talking about throttle; I think we wanted to check rt_queued in that
> > case.
> 
> Bah, clearly you also want to update on unthrottle.. but I think there's
> more buggered wrt throtteling.

Re: [PATCH v2] sched/rt: fix call to cpufreq_update_util

[Vincent Guittot]

Hi Peter,

On 17 May 2018 at 22:12, Vincent Guittot <vincent.guittot@linaro.org> wrote:
> Le Thursday 17 May 2018 à 11:32:06 (+0200), Peter Zijlstra a écrit :
>> On Thu, May 17, 2018 at 11:05:30AM +0200, Peter Zijlstra wrote:
>> > Hurm.. I think this is also wrong. See how dequeue_rt_stack() is also
>> > called from the enqueue path. Also, nothing calls cpufreq_update_util()
>> > on the throttle path now.
>
> Yes I missed the point that rt_entities were dequeued then re-enqueued when
> a task was either enqueued or dequeued.
>
> That's also means that enqueue_top_rt_rq() is always called when a task is
> enqueued or dequeued and also when groups are throttled or unthrottled
> In fact, the only point where it's not called, is when root rt_rq is
> throttled. So I have prepared the patch below which call cpufreq_update util
> in enqueue_top_rt_rq() and also when we throttle the root rt_rq.
> According to the tests I have done , it seems to work for enqueue/dequeue and
> throttle/unthrottle use cases.
>
> I have re-used your rt_rq_is_runnable() which takes into account rt_queued

What is the status for this problem ?

The patch below conflict with
b29bbbbff0d6 ('sched/cpufreq: always consider blocked FAIR utilization')
that has been merged in tip/sched/core

Do you want me to rebase it  ?

Regards,
Vincent

>
> ---
>  kernel/sched/cpufreq_schedutil.c |  2 +-
>  kernel/sched/rt.c                | 16 ++++++++++------
>  kernel/sched/sched.h             |  5 +++++
>  3 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index e13df95..1751f96 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -185,7 +185,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
>         struct rq *rq = cpu_rq(sg_cpu->cpu);
>         unsigned long util;
>
> -       if (rq->rt.rt_nr_running) {
> +       if (rt_rq_is_runnable(&rq->rt)) {
>                 util = sg_cpu->max;
>         } else {
>                 util = sg_cpu->util_dl;
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 7aef6b4..d6b9517 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -508,8 +508,11 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
>
>         rt_se = rt_rq->tg->rt_se[cpu];
>
> -       if (!rt_se)
> +       if (!rt_se) {
>                 dequeue_top_rt_rq(rt_rq);
> +               /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> +               cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
> +       }
>         else if (on_rt_rq(rt_se))
>                 dequeue_rt_entity(rt_se, 0);
>  }
> @@ -1001,8 +1004,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
>         sub_nr_running(rq, rt_rq->rt_nr_running);
>         rt_rq->rt_queued = 0;
>
> -       /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> -       cpufreq_update_util(rq, 0);
>  }
>
>  static void
> @@ -1014,11 +1015,14 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
>
>         if (rt_rq->rt_queued)
>                 return;
> -       if (rt_rq_throttled(rt_rq) || !rt_rq->rt_nr_running)
> +
> +       if (rt_rq_throttled(rt_rq))
>                 return;
>
> -       add_nr_running(rq, rt_rq->rt_nr_running);
> -       rt_rq->rt_queued = 1;
> +       if (rt_rq->rt_nr_running) {
> +               add_nr_running(rq, rt_rq->rt_nr_running);
> +               rt_rq->rt_queued = 1;
> +       }
>
>         /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
>         cpufreq_update_util(rq, 0);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index c9895d3..bbebcfe 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -609,6 +609,11 @@ struct rt_rq {
>  #endif
>  };
>
> +static inline bool rt_rq_is_runnable(struct rt_rq *rt_rq)
> +{
> +       return rt_rq->rt_queued && rt_rq->rt_nr_running;
> +}
> +
>  /* Deadline class' related fields in a runqueue */
>  struct dl_rq {
>         /* runqueue is an rbtree, ordered by deadline */
> --
> 2.7.4
>
>
>
>
>
>> >
>> > And talking about throttle; I think we wanted to check rt_queued in that
>> > case.
>>
>> Bah, clearly you also want to update on unthrottle.. but I think there's
>> more buggered wrt throtteling.
>
>
>
>

[PATCH v2] sched/rt: fix call to cpufreq_update_util

[Vincent Guittot]

With commit 8f111bc357aa ("cpufreq/schedutil: Rewrite CPUFREQ_RT support")
schedutil governor uses rq->rt.rt_nr_running to detect whether a RT task is
currently running on the CPU and to set frequency to max if necessary.

cpufreq_update_util() is called in enqueue/dequeue_top_rt_rq() but
rq->rt.rt_nr_running has not been updated yet when dequeue_top_rt_rq() is
called so schedutil still considers that a RT task is running when the
last task is dequeued. The update of rq->rt.rt_nr_running happens later
in dequeue_rt_stack().

In fact, we can take advantage of the sequence that the dequeue then
re-enqueue rt entities when a rt task is enqueued or dequeued;
As a result enqueue_top_rt_rq() is always called when a task is
enqueued or dequeued and also when groups are throttled or unthrottled.
The only place that not use enqueue_top_rt_rq() is when root rt_rq is
throttled.

Fixes: 8f111bc357aa ('cpufreq/schedutil: Rewrite CPUFREQ_RT support')
Cc: <stable@vger.kernel.org> # v4.16+
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/cpufreq_schedutil.c |  2 +-
 kernel/sched/rt.c                | 16 ++++++++++------
 kernel/sched/sched.h             |  5 +++++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 3cde464..c907fde 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -192,7 +192,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
 {
 	struct rq *rq = cpu_rq(sg_cpu->cpu);
 
-	if (rq->rt.rt_nr_running)
+	if (rt_rq_is_runnable(&rq->rt))
 		return sg_cpu->max;
 
 	/*
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 47556b0..5725670 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -508,8 +508,11 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
 
 	rt_se = rt_rq->tg->rt_se[cpu];
 
-	if (!rt_se)
+	if (!rt_se) {
 		dequeue_top_rt_rq(rt_rq);
+		/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
+		cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
+	}
 	else if (on_rt_rq(rt_se))
 		dequeue_rt_entity(rt_se, 0);
 }
@@ -1001,8 +1004,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
 	sub_nr_running(rq, rt_rq->rt_nr_running);
 	rt_rq->rt_queued = 0;
 
-	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq, 0);
 }
 
 static void
@@ -1014,11 +1015,14 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
 
 	if (rt_rq->rt_queued)
 		return;
-	if (rt_rq_throttled(rt_rq) || !rt_rq->rt_nr_running)
+
+	if (rt_rq_throttled(rt_rq))
 		return;
 
-	add_nr_running(rq, rt_rq->rt_nr_running);
-	rt_rq->rt_queued = 1;
+	if (rt_rq->rt_nr_running) {
+		add_nr_running(rq, rt_rq->rt_nr_running);
+		rt_rq->rt_queued = 1;
+	}
 
 	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
 	cpufreq_update_util(rq, 0);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 6601baf..27ddec3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -609,6 +609,11 @@ struct rt_rq {
 #endif
 };
 
+static inline bool rt_rq_is_runnable(struct rt_rq *rt_rq)
+{
+	return rt_rq->rt_queued && rt_rq->rt_nr_running;
+}
+
 /* Deadline class' related fields in a runqueue */
 struct dl_rq {
 	/* runqueue is an rbtree, ordered by deadline */
-- 
2.7.4

[tip:sched/core] sched/rt: Fix call to cpufreq_update_util()

[tip-bot for Vincent Guittot]

Commit-ID:  296b2ffe7fa9ed756c41415c6b1512bc4ad687b1
Gitweb:     https://git.kernel.org/tip/296b2ffe7fa9ed756c41415c6b1512bc4ad687b1
Author:     Vincent Guittot <vincent.guittot@linaro.org>
AuthorDate: Tue, 26 Jun 2018 15:53:22 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 3 Jul 2018 09:17:28 +0200

sched/rt: Fix call to cpufreq_update_util()

With commit:

  8f111bc357aa ("cpufreq/schedutil: Rewrite CPUFREQ_RT support")

the schedutil governor uses rq->rt.rt_nr_running to detect whether an
RT task is currently running on the CPU and to set frequency to max
if necessary.

cpufreq_update_util() is called in enqueue/dequeue_top_rt_rq() but
rq->rt.rt_nr_running has not been updated yet when dequeue_top_rt_rq() is
called so schedutil still considers that an RT task is running when the
last task is dequeued. The update of rq->rt.rt_nr_running happens later
in dequeue_rt_stack().

In fact, we can take advantage of the sequence that the dequeue then
re-enqueue rt entities when a rt task is enqueued or dequeued;
As a result enqueue_top_rt_rq() is always called when a task is
enqueued or dequeued and also when groups are throttled or unthrottled.
The only place that not use enqueue_top_rt_rq() is when root rt_rq is
throttled.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: efault@gmx.de
Cc: juri.lelli@redhat.com
Cc: patrick.bellasi@arm.com
Cc: viresh.kumar@linaro.org
Fixes: 8f111bc357aa ('cpufreq/schedutil: Rewrite CPUFREQ_RT support')
Link: http://lkml.kernel.org/r/1530021202-21695-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/cpufreq_schedutil.c |  2 +-
 kernel/sched/rt.c                | 16 ++++++++++------
 kernel/sched/sched.h             |  5 +++++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 3cde46483f0a..c907fde01eaa 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -192,7 +192,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
 {
 	struct rq *rq = cpu_rq(sg_cpu->cpu);
 
-	if (rq->rt.rt_nr_running)
+	if (rt_rq_is_runnable(&rq->rt))
 		return sg_cpu->max;
 
 	/*
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 47556b0c9a95..572567078b60 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -508,8 +508,11 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
 
 	rt_se = rt_rq->tg->rt_se[cpu];
 
-	if (!rt_se)
+	if (!rt_se) {
 		dequeue_top_rt_rq(rt_rq);
+		/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
+		cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
+	}
 	else if (on_rt_rq(rt_se))
 		dequeue_rt_entity(rt_se, 0);
 }
@@ -1001,8 +1004,6 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
 	sub_nr_running(rq, rt_rq->rt_nr_running);
 	rt_rq->rt_queued = 0;
 
-	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq, 0);
 }
 
 static void
@@ -1014,11 +1015,14 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
 
 	if (rt_rq->rt_queued)
 		return;
-	if (rt_rq_throttled(rt_rq) || !rt_rq->rt_nr_running)
+
+	if (rt_rq_throttled(rt_rq))
 		return;
 
-	add_nr_running(rq, rt_rq->rt_nr_running);
-	rt_rq->rt_queued = 1;
+	if (rt_rq->rt_nr_running) {
+		add_nr_running(rq, rt_rq->rt_nr_running);
+		rt_rq->rt_queued = 1;
+	}
 
 	/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
 	cpufreq_update_util(rq, 0);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 6601baf2361c..27ddec334601 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -609,6 +609,11 @@ struct rt_rq {
 #endif
 };
 
+static inline bool rt_rq_is_runnable(struct rt_rq *rt_rq)
+{
+	return rt_rq->rt_queued && rt_rq->rt_nr_running;
+}
+
 /* Deadline class' related fields in a runqueue */
 struct dl_rq {
 	/* runqueue is an rbtree, ordered by deadline */