[PATCH 1/2] cpufreq: schedutil: Fix superfluous updates caused by need_freq_update

[Sultan Alsawaf]

From: "Sultan Alsawaf (unemployed)" <sultan@xxxxxxxxxxxxxxx>

A redundant frequency update is only truly needed when there is a policy
limits change with a driver that specifies CPUFREQ_NEED_UPDATE_LIMITS.

In spite of that, drivers specifying CPUFREQ_NEED_UPDATE_LIMITS receive a
frequency update _all the time_, not just for a policy limits change,
because need_freq_update is never cleared.

Furthermore, ignore_dl_rate_limit()'s usage of need_freq_update also leads
to a redundant frequency update, regardless of whether or not the driver
specifies CPUFREQ_NEED_UPDATE_LIMITS, when the next chosen frequency is the
same as the current one.

Fix the superfluous updates by only honoring CPUFREQ_NEED_UPDATE_LIMITS
when there's a policy limits change, and clearing need_freq_update when a
requisite redundant update occurs.

This is neatly achieved by moving up the CPUFREQ_NEED_UPDATE_LIMITS test
and instead setting need_freq_update to false in sugov_update_next_freq().

Signed-off-by: Sultan Alsawaf (unemployed) <sultan@xxxxxxxxxxxxxxx>
---
 kernel/sched/cpufreq_schedutil.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 28c77904ea74..e51d5ce730be 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -83,7 +83,7 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
 
 	if (unlikely(sg_policy->limits_changed)) {
 		sg_policy->limits_changed = false;
-		sg_policy->need_freq_update = true;
+		sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
 		return true;
 	}
 
@@ -96,7 +96,7 @@ static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
 				   unsigned int next_freq)
 {
 	if (sg_policy->need_freq_update)
-		sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
+		sg_policy->need_freq_update = false;
 	else if (sg_policy->next_freq == next_freq)
 		return false;
 
-- 
2.47.1