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Message-Id: <20240820163512.1096301-2-qyousef@layalina.io>
Date: Tue, 20 Aug 2024 17:34:57 +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 01/16] sched: cpufreq: Rename map_util_perf to sugov_apply_dvfs_headroom
We are providing headroom for the utilization to grow until the next
decision point to pick the next frequency. Give the function a better
name and give it some documentation. It is not really mapping anything.
Also move it to cpufreq_schedutil.c. This function relies on updating
util signal appropriately to give a headroom to grow. This is tied to
schedutil and scheduler and not something that can be shared with other
governors.
Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
Acked-by: Rafael J. Wysocki <rafael@...nel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Qais Yousef <qyousef@...alina.io>
---
include/linux/sched/cpufreq.h | 5 -----
kernel/sched/cpufreq_schedutil.c | 20 +++++++++++++++++++-
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
index bdd31ab93bc5..d01755d3142f 100644
--- a/include/linux/sched/cpufreq.h
+++ b/include/linux/sched/cpufreq.h
@@ -28,11 +28,6 @@ static inline unsigned long map_util_freq(unsigned long util,
{
return freq * util / cap;
}
-
-static inline unsigned long map_util_perf(unsigned long util)
-{
- return util + (util >> 2);
-}
#endif /* CONFIG_CPU_FREQ */
#endif /* _LINUX_SCHED_CPUFREQ_H */
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index eece6244f9d2..575df3599813 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -178,12 +178,30 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
return cpufreq_driver_resolve_freq(policy, freq);
}
+/*
+ * DVFS decision are made at discrete points. If CPU stays busy, the util will
+ * continue to grow, which means it could need to run at a higher frequency
+ * before the next decision point was reached. IOW, we can't follow the util as
+ * it grows immediately, but there's a delay before we issue a request to go to
+ * higher frequency. The headroom caters for this delay so the system continues
+ * to run at adequate performance point.
+ *
+ * This function provides enough headroom to provide adequate performance
+ * assuming the CPU continues to be busy.
+ *
+ * At the moment it is a constant multiplication with 1.25.
+ */
+static inline unsigned long sugov_apply_dvfs_headroom(unsigned long util)
+{
+ return util + (util >> 2);
+}
+
unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
unsigned long min,
unsigned long max)
{
/* Add dvfs headroom to actual utilization */
- actual = map_util_perf(actual);
+ actual = sugov_apply_dvfs_headroom(actual);
/* Actually we don't need to target the max performance */
if (actual < max)
max = actual;
--
2.34.1
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