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Date: Thu, 17 May 2018 11:05:30 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: mingo@...nel.org, linux-kernel@...r.kernel.org,
patrick.bellasi@....com, viresh.kumar@...aro.org,
tglx@...utronix.de, efault@....de, juri.lelli@...hat.com,
"# v4 . 16+" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] sched/rt: fix call to cpufreq_update_util
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@...r.kernel.org> # v4.16+
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.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 */
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