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From: Qais Yousef <qyousef@layalina.io>
To: "Rafael J. Wysocki" <rafael@kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Juri Lelli <juri.lelli@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Ben Segall <bsegall@google.com>,
	Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Christian Loehle <christian.loehle@arm.com>,
	linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Qais Yousef <qyousef@layalina.io>
Subject: [RFC PATCH] sched: Consolidate cpufreq updates
Date: Sun, 24 Mar 2024 02:01:39 +0000
Message-Id: <20240324020139.1032473-1-qyousef@layalina.io>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

Improve the interaction with cpufreq governors by making the
cpufreq_update_util() calls more intentional.

At the moment we send them when load is updated for CFS, bandwidth for
DL and at enqueue/dequeue for RT. But this can lead to too many updates
sent in a short period of time and potentially be ignored at a critical
moment due to the rate_limit_us in schedutil.

For example, simultaneous task enqueue on the CPU where 2nd task is
bigger and requires higher freq. The trigger to cpufreq_update_util() by
the first task will lead to dropping the 2nd request until tick. Or
another CPU in the same policy triggers a freq update shortly after.

Updates at enqueue for RT are not strictly required. Though they do help
to reduce the delay for switching the frequency and the potential
observation of lower frequency during this delay. But current logic
doesn't intentionally (at least to my understanding) try to speed up the
request.

To help reduce the amount of cpufreq updates and make them more
purposeful, consolidate them into these locations:

1. context_switch()
2. task_tick_fair()
3. {attach, detach}_entity_load_avg()
4. update_blocked_averages()

The update at context switch should help guarantee that DL and RT get
the right frequency straightaway when they're RUNNING. As mentioned
though the update will happen slightly after enqueue_task(); though in
an ideal world these tasks should be RUNNING ASAP and this additional
delay should be negligible. For fair tasks we need to make sure we send
a single update for every decay for the root cfs_rq. Any changes to the
rq will be deferred until the next task is ready to run, or we hit TICK.
But we are guaranteed the task is running at a level that meets its
requirements after enqueue.

To guarantee RT and DL tasks updates are never missed, we add a new
SCHED_CPUFREQ_FORCE_UPDATE to ignore the rate_limit_us. If we are
already running at the right freq, the governor will end up doing
nothing, but we eliminate the risk of the task ending up accidentally
running at the wrong freq due to rate_limit_us.

Similarly for iowait boost. We also handle a case of a boost reset
prematurely by adding a guard against TICK_NSEC in sugov_iowait_apply()
in similar fashion to sugov_iowait_reset().

The new SCHED_CPUFREQ_FORCE_UPDATE should not impact the rate limit
time stamps otherwise we can end up delaying updates for normal
requests.

We also teach sugov to ignore cpufreq updates from its sugov workers. It
doesn't make sense for the kworker that applies the frequency update
(which is a DL task) to trigger a frequency update itself.

There's room for an optimization that I haven't pursued yet (but plan to
follow up with in the future) which is not to do an update for RT/DL if
the frequency level is already the same. sugov currently already handles
this, but since we force ignoring rate limit now, it would be ideal not
to force too many frequency updates in a row if there's not much to do.
We need to compare uclamp_min values for RT and bandwidth values for DL
between next and prev tasks.

The update at task_tick_fair will guarantee that the governor will
follow any updates to load for tasks/CPU or due to new enqueues/dequeues
to the rq. Since DL and RT always run at constant frequencies and have
no load tracking, this is only required for fair tasks.

The update at attach/detach_entity_load_avg() will ensure we adapt to
big changes when tasks are added/removed from cgroups.

The update at update_blocked_averages() will ensure we decay frequency
as the CPU becomes idle for long enough.

I am contemplating to make all updates except for CFS at context switch
a forced updates. I'd welcome thoughts. Context switch should be our
major drive for frequency change, and the other operations should be
treated as out-of-line updates that must be honoured and not be
accidentally dropped by rate limit. Contemplating the impact on shared
policies if we go down that route too. Thoughts would be appreciated.

To make sure governors that don't register a cpufreq_update_util()
handler aren't impacted, we protect the call with a static key to ensure
that it is only active when the current governor makes use of it.

Results of `perf stat --repeat 10 perf bench sched pipe` on AMD 3900X to
verify any potential overhead because of the addition at context switch

Before:
-------

	Performance counter stats for 'perf bench sched pipe' (10 runs):

		 16,839.74 msec task-clock:u              #    1.158 CPUs utilized            ( +-  0.52% )
			 0      context-switches:u        #    0.000 /sec
			 0      cpu-migrations:u          #    0.000 /sec
		     1,390      page-faults:u             #   83.903 /sec                     ( +-  0.06% )
	       333,773,107      cycles:u                  #    0.020 GHz                      ( +-  0.70% )  (83.72%)
		67,050,466      stalled-cycles-frontend:u #   19.94% frontend cycles idle     ( +-  2.99% )  (83.23%)
		37,763,775      stalled-cycles-backend:u  #   11.23% backend cycles idle      ( +-  2.18% )  (83.09%)
		84,456,137      instructions:u            #    0.25  insn per cycle
							  #    0.83  stalled cycles per insn  ( +-  0.02% )  (83.01%)
		34,097,544      branches:u                #    2.058 M/sec                    ( +-  0.02% )  (83.52%)
		 8,038,902      branch-misses:u           #   23.59% of all branches          ( +-  0.03% )  (83.44%)

		   14.5464 +- 0.0758 seconds time elapsed  ( +-  0.52% )

After:
-------

	Performance counter stats for 'perf bench sched pipe' (10 runs):

		 16,219.58 msec task-clock:u              #    1.130 CPUs utilized            ( +-  0.80% )
			 0      context-switches:u        #    0.000 /sec
			 0      cpu-migrations:u          #    0.000 /sec
		     1,391      page-faults:u             #   85.163 /sec                     ( +-  0.06% )
	       342,768,312      cycles:u                  #    0.021 GHz                      ( +-  0.63% )  (83.36%)
		66,231,208      stalled-cycles-frontend:u #   18.91% frontend cycles idle     ( +-  2.34% )  (83.95%)
		39,055,410      stalled-cycles-backend:u  #   11.15% backend cycles idle      ( +-  1.80% )  (82.73%)
		84,475,662      instructions:u            #    0.24  insn per cycle
							  #    0.82  stalled cycles per insn  ( +-  0.02% )  (83.05%)
		34,067,160      branches:u                #    2.086 M/sec                    ( +-  0.02% )  (83.67%)
		 8,042,888      branch-misses:u           #   23.60% of all branches          ( +-  0.07% )  (83.25%)

		    14.358 +- 0.116 seconds time elapsed  ( +-  0.81% )

Note worthy that we still have the following race condition on systems
that have shared policy:

* CPUs with shared policy can end up sending simultaneous cpufreq
  updates requests where the 2nd one will be unlucky and get blocked by
  the rate_limit_us (schedutil).

We can potentially address this limitation later, but it is out of the
scope of this patch.

Signed-off-by: Qais Yousef <qyousef@layalina.io>
---
 include/linux/sched/cpufreq.h    |  3 +-
 kernel/sched/core.c              | 51 +++++++++++++++++++++++
 kernel/sched/cpufreq.c           |  5 +++
 kernel/sched/cpufreq_schedutil.c | 71 +++++++++++++++++++++++++-------
 kernel/sched/deadline.c          |  4 --
 kernel/sched/fair.c              | 53 ++++--------------------
 kernel/sched/rt.c                |  8 +---
 kernel/sched/sched.h             | 10 +++++
 8 files changed, 133 insertions(+), 72 deletions(-)

diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
index bdd31ab93bc5..2d0a45aba16f 100644
--- a/include/linux/sched/cpufreq.h
+++ b/include/linux/sched/cpufreq.h
@@ -8,7 +8,8 @@
  * Interface between cpufreq drivers and the scheduler:
  */
 
-#define SCHED_CPUFREQ_IOWAIT	(1U << 0)
+#define SCHED_CPUFREQ_IOWAIT		(1U << 0)
+#define SCHED_CPUFREQ_FORCE_UPDATE	(1U << 1) /* ignore transition_delay_us */
 
 #ifdef CONFIG_CPU_FREQ
 struct cpufreq_policy;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 929fce69f555..563cb61dbf79 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5134,6 +5134,52 @@ static inline void balance_callbacks(struct rq *rq, struct balance_callback *hea
 
 #endif
 
+static inline void update_cpufreq_ctx_switch(struct rq *rq)
+{
+#ifdef CONFIG_CPU_FREQ
+	unsigned int flags = 0;
+
+	if (!static_branch_likely(&cpufreq_update_enabled))
+		return;
+
+#ifdef CONFIG_SMP
+	if (unlikely(current->sched_class == &stop_sched_class))
+		return;
+#endif
+
+	if (unlikely(current->sched_class == &idle_sched_class))
+		return;
+
+	if (unlikely(task_has_idle_policy(current)))
+		return;
+
+	if (likely(fair_policy(current->policy))) {
+
+		if (unlikely(current->in_iowait)) {
+			flags |= SCHED_CPUFREQ_IOWAIT | SCHED_CPUFREQ_FORCE_UPDATE;
+			goto force_update;
+		}
+
+#ifdef CONFIG_SMP
+		/*
+		 * Allow cpufreq updates once for every update_load_avg() decay.
+		 */
+		if (unlikely(rq->cfs.decayed)) {
+			rq->cfs.decayed = false;
+			goto force_update;
+		}
+#endif
+		return;
+	}
+
+	/* RT and DL should always send a freq update */
+	flags |= SCHED_CPUFREQ_FORCE_UPDATE;
+
+force_update:
+	cpufreq_update_util(rq, flags);
+#endif
+}
+
 static inline void
 prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
 {
@@ -5160,6 +5206,11 @@ static inline void finish_lock_switch(struct rq *rq)
 	 */
 	spin_acquire(&__rq_lockp(rq)->dep_map, 0, 0, _THIS_IP_);
 	__balance_callbacks(rq);
+	/*
+	 * Request freq update after __balance_callbacks to take into account
+	 * any changes to rq.
+	 */
+	update_cpufreq_ctx_switch(rq);
 	raw_spin_rq_unlock_irq(rq);
 }
 
diff --git a/kernel/sched/cpufreq.c b/kernel/sched/cpufreq.c
index 5252fb191fae..369eb2c8c6ae 100644
--- a/kernel/sched/cpufreq.c
+++ b/kernel/sched/cpufreq.c
@@ -8,6 +8,8 @@
 
 DEFINE_PER_CPU(struct update_util_data __rcu *, cpufreq_update_util_data);
 
+DEFINE_STATIC_KEY_FALSE(cpufreq_update_enabled);
+
 /**
  * cpufreq_add_update_util_hook - Populate the CPU's update_util_data pointer.
  * @cpu: The CPU to set the pointer for.
@@ -33,6 +35,8 @@ void cpufreq_add_update_util_hook(int cpu, struct update_util_data *data,
 	if (WARN_ON(!data || !func))
 		return;
 
+	static_branch_enable(&cpufreq_update_enabled);
+
 	if (WARN_ON(per_cpu(cpufreq_update_util_data, cpu)))
 		return;
 
@@ -54,6 +58,7 @@ EXPORT_SYMBOL_GPL(cpufreq_add_update_util_hook);
 void cpufreq_remove_update_util_hook(int cpu)
 {
 	rcu_assign_pointer(per_cpu(cpufreq_update_util_data, cpu), NULL);
+	static_branch_disable(&cpufreq_update_enabled);
 }
 EXPORT_SYMBOL_GPL(cpufreq_remove_update_util_hook);
 
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index eece6244f9d2..2f83ac898c34 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -59,7 +59,8 @@ static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu);
 
 /************************ Governor internals ***********************/
 
-static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
+static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time,
+				     unsigned int flags)
 {
 	s64 delta_ns;
 
@@ -87,13 +88,16 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
 		return true;
 	}
 
+	if (unlikely(flags & SCHED_CPUFREQ_FORCE_UPDATE))
+		return true;
+
 	delta_ns = time - sg_policy->last_freq_update_time;
 
 	return delta_ns >= sg_policy->freq_update_delay_ns;
 }
 
 static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
-				   unsigned int next_freq)
+				   unsigned int next_freq, unsigned int flags)
 {
 	if (sg_policy->need_freq_update)
 		sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
@@ -101,7 +105,9 @@ static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
 		return false;
 
 	sg_policy->next_freq = next_freq;
-	sg_policy->last_freq_update_time = time;
+
+	if (!unlikely(flags & SCHED_CPUFREQ_FORCE_UPDATE))
+		sg_policy->last_freq_update_time = time;
 
 	return true;
 }
@@ -249,9 +255,10 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
 			       unsigned int flags)
 {
 	bool set_iowait_boost = flags & SCHED_CPUFREQ_IOWAIT;
+	bool forced_update = flags & SCHED_CPUFREQ_FORCE_UPDATE;
 
 	/* Reset boost if the CPU appears to have been idle enough */
-	if (sg_cpu->iowait_boost &&
+	if (sg_cpu->iowait_boost && !forced_update &&
 	    sugov_iowait_reset(sg_cpu, time, set_iowait_boost))
 		return;
 
@@ -294,17 +301,29 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
  * being more conservative on tasks which does sporadic IO operations.
  */
 static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
-			       unsigned long max_cap)
+			       unsigned long max_cap, unsigned int flags)
 {
+	bool forced_update = flags & SCHED_CPUFREQ_FORCE_UPDATE;
+	s64 delta_ns = time - sg_cpu->last_update;
+
 	/* No boost currently required */
 	if (!sg_cpu->iowait_boost)
 		return 0;
 
+	if (forced_update)
+		goto apply_boost;
+
 	/* Reset boost if the CPU appears to have been idle enough */
 	if (sugov_iowait_reset(sg_cpu, time, false))
 		return 0;
 
 	if (!sg_cpu->iowait_boost_pending) {
+		/*
+		 * Reduce boost only if a tick has elapsed since last request.
+		 */
+		if (delta_ns <= TICK_NSEC)
+			goto apply_boost;
+
 		/*
 		 * No boost pending; reduce the boost value.
 		 */
@@ -315,6 +334,7 @@ static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
 		}
 	}
 
+apply_boost:
 	sg_cpu->iowait_boost_pending = false;
 
 	/*
@@ -351,17 +371,28 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,
 					      u64 time, unsigned long max_cap,
 					      unsigned int flags)
 {
+	bool forced_update = flags & SCHED_CPUFREQ_FORCE_UPDATE;
+	struct sugov_policy *sg_policy = sg_cpu->sg_policy;
+	bool iowait_boost = flags & SCHED_CPUFREQ_IOWAIT;
 	unsigned long boost;
 
+	/*
+	 * Forced updates are initiated by iowait and RT/DL tasks. If the
+	 * latter, verify that it's not our worker thread that is initiating
+	 * this forced update.
+	 */
+	if (forced_update && !iowait_boost && current == sg_policy->thread)
+		return false;
+
 	sugov_iowait_boost(sg_cpu, time, flags);
 	sg_cpu->last_update = time;
 
 	ignore_dl_rate_limit(sg_cpu);
 
-	if (!sugov_should_update_freq(sg_cpu->sg_policy, time))
+	if (!sugov_should_update_freq(sg_cpu->sg_policy, time, flags))
 		return false;
 
-	boost = sugov_iowait_apply(sg_cpu, time, max_cap);
+	boost = sugov_iowait_apply(sg_cpu, time, max_cap, flags);
 	sugov_get_util(sg_cpu, boost);
 
 	return true;
@@ -397,7 +428,7 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time,
 		sg_policy->cached_raw_freq = cached_freq;
 	}
 
-	if (!sugov_update_next_freq(sg_policy, time, next_f))
+	if (!sugov_update_next_freq(sg_policy, time, next_f, flags))
 		return;
 
 	/*
@@ -449,10 +480,12 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
 	cpufreq_driver_adjust_perf(sg_cpu->cpu, sg_cpu->bw_min,
 				   sg_cpu->util, max_cap);
 
-	sg_cpu->sg_policy->last_freq_update_time = time;
+	if (!unlikely(flags & SCHED_CPUFREQ_FORCE_UPDATE))
+		sg_cpu->sg_policy->last_freq_update_time = time;
 }
 
-static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
+static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time,
+					   unsigned int flags)
 {
 	struct sugov_policy *sg_policy = sg_cpu->sg_policy;
 	struct cpufreq_policy *policy = sg_policy->policy;
@@ -465,7 +498,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
 		struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j);
 		unsigned long boost;
 
-		boost = sugov_iowait_apply(j_sg_cpu, time, max_cap);
+		boost = sugov_iowait_apply(j_sg_cpu, time, max_cap, flags);
 		sugov_get_util(j_sg_cpu, boost);
 
 		util = max(j_sg_cpu->util, util);
@@ -478,9 +511,19 @@ static void
 sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags)
 {
 	struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
+	bool forced_update = flags & SCHED_CPUFREQ_FORCE_UPDATE;
 	struct sugov_policy *sg_policy = sg_cpu->sg_policy;
+	bool iowait_boost = flags & SCHED_CPUFREQ_IOWAIT;
 	unsigned int next_f;
 
+	/*
+	 * Forced updates are initiated by iowait and RT/DL tasks. If the
+	 * latter, verify that it's not our worker thread that is initiating
+	 * this forced update.
+	 */
+	if (forced_update && !iowait_boost && current == sg_policy->thread)
+		return;
+
 	raw_spin_lock(&sg_policy->update_lock);
 
 	sugov_iowait_boost(sg_cpu, time, flags);
@@ -488,10 +531,10 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags)
 
 	ignore_dl_rate_limit(sg_cpu);
 
-	if (sugov_should_update_freq(sg_policy, time)) {
-		next_f = sugov_next_freq_shared(sg_cpu, time);
+	if (sugov_should_update_freq(sg_policy, time, flags)) {
+		next_f = sugov_next_freq_shared(sg_cpu, time, flags);
 
-		if (!sugov_update_next_freq(sg_policy, time, next_f))
+		if (!sugov_update_next_freq(sg_policy, time, next_f, flags))
 			goto unlock;
 
 		if (sg_policy->policy->fast_switch_enabled)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a04a436af8cc..02c9c2488091 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -252,8 +252,6 @@ void __add_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
 	dl_rq->running_bw += dl_bw;
 	SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
 	SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
-	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
 }
 
 static inline
@@ -266,8 +264,6 @@ void __sub_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
 	SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
 	if (dl_rq->running_bw > old)
 		dl_rq->running_bw = 0;
-	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
-	cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
 }
 
 static inline
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c8e50fbac345..a0692e308d2d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3982,29 +3982,6 @@ static inline void update_cfs_group(struct sched_entity *se)
 }
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
-static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
-{
-	struct rq *rq = rq_of(cfs_rq);
-
-	if (&rq->cfs == cfs_rq) {
-		/*
-		 * There are a few boundary cases this might miss but it should
-		 * get called often enough that that should (hopefully) not be
-		 * a real problem.
-		 *
-		 * It will not get called when we go idle, because the idle
-		 * thread is a different class (!fair), nor will the utilization
-		 * number include things like RT tasks.
-		 *
-		 * As is, the util number is not freq-invariant (we'd have to
-		 * implement arch_scale_freq_capacity() for that).
-		 *
-		 * See cpu_util_cfs().
-		 */
-		cpufreq_update_util(rq, flags);
-	}
-}
-
 #ifdef CONFIG_SMP
 static inline bool load_avg_is_decayed(struct sched_avg *sa)
 {
@@ -4682,7 +4659,7 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 
 	add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);
 
-	cfs_rq_util_change(cfs_rq, 0);
+	cpufreq_update_util(rq_of(cfs_rq), 0);
 
 	trace_pelt_cfs_tp(cfs_rq);
 }
@@ -4712,7 +4689,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 
 	add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);
 
-	cfs_rq_util_change(cfs_rq, 0);
+	cpufreq_update_util(rq_of(cfs_rq), 0);
 
 	trace_pelt_cfs_tp(cfs_rq);
 }
@@ -4729,7 +4706,6 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
 	u64 now = cfs_rq_clock_pelt(cfs_rq);
-	int decayed;
 
 	/*
 	 * Track task load average for carrying it to new CPU after migrated, and
@@ -4738,8 +4714,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
 		__update_load_avg_se(now, cfs_rq, se);
 
-	decayed  = update_cfs_rq_load_avg(now, cfs_rq);
-	decayed |= propagate_entity_load_avg(se);
+	cfs_rq->decayed  = update_cfs_rq_load_avg(now, cfs_rq);
+	cfs_rq->decayed |= propagate_entity_load_avg(se);
 
 	if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
 
@@ -4760,11 +4736,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 		 */
 		detach_entity_load_avg(cfs_rq, se);
 		update_tg_load_avg(cfs_rq);
-	} else if (decayed) {
-		cfs_rq_util_change(cfs_rq, 0);
-
-		if (flags & UPDATE_TG)
-			update_tg_load_avg(cfs_rq);
+	} else if (cfs_rq->decayed && (flags & UPDATE_TG)) {
+		update_tg_load_avg(cfs_rq);
 	}
 }
 
@@ -5126,7 +5099,6 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
 
 static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
 {
-	cfs_rq_util_change(cfs_rq, 0);
 }
 
 static inline void remove_entity_load_avg(struct sched_entity *se) {}
@@ -6716,14 +6688,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	 */
 	util_est_enqueue(&rq->cfs, p);
 
-	/*
-	 * If in_iowait is set, the code below may not trigger any cpufreq
-	 * utilization updates, so do it here explicitly with the IOWAIT flag
-	 * passed.
-	 */
-	if (p->in_iowait)
-		cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
-
 	for_each_sched_entity(se) {
 		if (se->on_rq)
 			break;
@@ -9282,10 +9246,6 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
 	unsigned long thermal_pressure;
 	bool decayed;
 
-	/*
-	 * update_load_avg() can call cpufreq_update_util(). Make sure that RT,
-	 * DL and IRQ signals have been updated before updating CFS.
-	 */
 	curr_class = rq->curr->sched_class;
 
 	thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
@@ -12623,6 +12583,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 
 	update_misfit_status(curr, rq);
 	update_overutilized_status(task_rq(curr));
+	cpufreq_update_util(rq, 0);
 
 	task_tick_core(rq, curr);
 }
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..fe6d8b0ffa95 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -556,11 +556,8 @@ 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, rt_rq->rt_nr_running);
-		/* 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);
 }
@@ -1065,9 +1062,6 @@ 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
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 41024c1c49b4..6a6de92448d1 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -618,6 +618,11 @@ struct cfs_rq {
 		unsigned long	runnable_avg;
 	} removed;
 
+	/*
+	 * Store whether last update_load_avg() has decayed
+	 */
+	bool			decayed;
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	u64			last_update_tg_load_avg;
 	unsigned long		tg_load_avg_contrib;
@@ -2961,6 +2966,8 @@ static inline u64 irq_time_read(int cpu)
 #ifdef CONFIG_CPU_FREQ
 DECLARE_PER_CPU(struct update_util_data __rcu *, cpufreq_update_util_data);
 
+DECLARE_STATIC_KEY_FALSE(cpufreq_update_enabled);
+
 /**
  * cpufreq_update_util - Take a note about CPU utilization changes.
  * @rq: Runqueue to carry out the update for.
@@ -2987,6 +2994,9 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags)
 {
 	struct update_util_data *data;
 
+	if (!static_branch_likely(&cpufreq_update_enabled))
+		return;
+
 	data = rcu_dereference_sched(*per_cpu_ptr(&cpufreq_update_util_data,
 						  cpu_of(rq)));
 	if (data)
-- 
2.34.1