linux-kernel - [PATCH] sched: cpufreq_schedutil: restore cached freq when next

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Message-Id: <20201016181722.884812-1-wvw@google.com>
Date:   Fri, 16 Oct 2020 11:17:22 -0700
From:   Wei Wang <wvw@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     wei.vince.wang@...il.com, viresh.kumar@...aro.org,
        qperret@...gle.com, rafael@...nel.org, Wei Wang <wvw@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] sched: cpufreq_schedutil: restore cached freq when next_f is
 not changed

We have the raw cached freq to reduce the chance in calling cpufreq
driver where it could be costly in some arch/SoC.

Currently, the raw cached freq will be reset when next_f is changed for
correctness. This patch changes it to maintain the cached value instead
of dropping it to honor the purpose of the cached value.

This is adapted from https://android-review.googlesource.com/1352810/

Signed-off-by: Wei Wang <wvw@...gle.com>
---
 kernel/sched/cpufreq_schedutil.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 5ae7b4e6e8d6..e254745a82cb 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -441,6 +441,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
 	unsigned long util, max;
 	unsigned int next_f;
 	bool busy;
+	unsigned int cached_freq = sg_policy->cached_raw_freq;
 
 	sugov_iowait_boost(sg_cpu, time, flags);
 	sg_cpu->last_update = time;
@@ -464,8 +465,8 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
 	if (busy && next_f < sg_policy->next_freq) {
 		next_f = sg_policy->next_freq;
 
-		/* Reset cached freq as next_freq has changed */
-		sg_policy->cached_raw_freq = 0;
+		/* Restore cached freq as next_freq has changed */
+		sg_policy->cached_raw_freq = cached_freq;
 	}
 
 	/*
-- 
2.29.0.rc1.297.gfa9743e501-goog