linux-kernel - [RFC PATCH 13/16] sched/schedutil: Take into account waiting_avg in apply_dvfs

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Message-Id: <20240820163512.1096301-14-qyousef@layalina.io>
Date: Tue, 20 Aug 2024 17:35:09 +0100
From: Qais Yousef <qyousef@...alina.io>
To: Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>
Cc: Juri Lelli <juri.lelli@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	John Stultz <jstultz@...gle.com>,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Qais Yousef <qyousef@...alina.io>
Subject: [RFC PATCH 13/16] sched/schedutil: Take into account waiting_avg in apply_dvfs_headroom

We now have three sources of delays.

	1. How often we send cpufreq_updates
	2. How often we update util_avg
	3. How long tasks wait in RUNNABLE to become RUNNING

The headroom should cater for all this type of delays to ensure the
system is running at adequate performance point.

We want to pick the maximum headroom required by any of these sources of
delays.

TODO: the signal should use task clock not pelt as this should be
real time based and we don't care about invariance.

Signed-off-by: Qais Yousef <qyousef@...alina.io>
---
 kernel/sched/cpufreq_schedutil.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 94e35b7c972d..318b09bc4ab1 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -259,10 +259,15 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
  * dvfs_update_delay of the cpufreq governor or min(curr.se.slice, TICK_US),
  * whichever is higher.
  *
+ * Also take into accounting how long tasks have been waiting in runnable but
+ * !running state. If it is high, it means we need higher DVFS headroom to
+ * reduce it.
+ *
  * XXX: Should we provide headroom when the util is decaying?
  */
 static inline unsigned long sugov_apply_dvfs_headroom(unsigned long util,  int cpu)
 {
+	unsigned long update_headroom, waiting_headroom;
 	struct rq *rq = cpu_rq(cpu);
 	u64 delay;
 
@@ -276,7 +281,10 @@ static inline unsigned long sugov_apply_dvfs_headroom(unsigned long util,  int c
 		delay = TICK_USEC;
 	delay = max(delay, per_cpu(dvfs_update_delay, cpu));
 
-	return approximate_util_avg(util, delay);
+	update_headroom = approximate_util_avg(util, delay);
+	waiting_headroom = util + READ_ONCE(rq->cfs.avg.waiting_avg);
+
+	return max(update_headroom, waiting_headroom);
 }
 
 unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
-- 
2.34.1