linux-kernel - [PATCH] cpufreq: schedutil: Don't ignore limit changes when util is unchanged

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Message-ID: <20250410024439.20859-1-sultan@kerneltoast.com>
Date: Wed,  9 Apr 2025 19:44:37 -0700
From: Sultan Alsawaf <sultan@...neltoast.com>
To: 
Cc: Stephan Gerhold <stephan.gerhold@...aro.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	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>,
	Valentin Schneider <vschneid@...hat.com>,
	Christian Loehle <christian.loehle@....com>,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] cpufreq: schedutil: Don't ignore limit changes when util is unchanged

From: Sultan Alsawaf <sultan@...neltoast.com>

When utilization is unchanged, a policy limits update is ignored unless
CPUFREQ_NEED_UPDATE_LIMITS is set. This occurs because limits_changed
depends on the old broken behavior of need_freq_update to trigger a call
into cpufreq_driver_resolve_freq() to evaluate the changed policy limits.

After fixing need_freq_update, limit changes are ignored without
CPUFREQ_NEED_UPDATE_LIMITS, at least until utilization changes enough to
make map_util_freq() return something different.

Fix the ignored limit changes by preserving the value of limits_changed
until get_next_freq() is called, so limits_changed can trigger a call to
cpufreq_driver_resolve_freq().

Reported-and-tested-by: Stephan Gerhold <stephan.gerhold@...aro.org>
Link: https://lore.kernel.org/lkml/Z_Tlc6Qs-tYpxWYb@linaro.org
Fixes: 8e461a1cb43d6 ("cpufreq: schedutil: Fix superfluous updates caused by need_freq_update")
Signed-off-by: Sultan Alsawaf <sultan@...neltoast.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 1a19d69b91ed3..f37b999854d52 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -82,7 +82,6 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
 		return false;
 
 	if (unlikely(sg_policy->limits_changed)) {
-		sg_policy->limits_changed = false;
 		sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
 		return true;
 	}
@@ -171,9 +170,11 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
 	freq = get_capacity_ref_freq(policy);
 	freq = map_util_freq(util, freq, max);
 
-	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
+	if (freq == sg_policy->cached_raw_freq && !sg_policy->limits_changed &&
+	    !sg_policy->need_freq_update)
 		return sg_policy->next_freq;
 
+	sg_policy->limits_changed = false;
 	sg_policy->cached_raw_freq = freq;
 	return cpufreq_driver_resolve_freq(policy, freq);
 }
-- 
2.49.0