linux-kernel - [PATCH v2 3/6] cpufreq/sched: Set need_freq_update in ignore_dl_rate

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Message-ID: <10666429.nUPlyArG6x@rjwysocki.net>
Date: Tue, 15 Apr 2025 12:00:52 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Mario Limonciello <mario.limonciello@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Christian Loehle <christian.loehle@....com>,
 Sultan Alsawaf <sultan@...neltoast.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Valentin Schneider <vschneid@...hat.com>, Ingo Molnar <mingo@...hat.com>
Subject:
 [PATCH v2 3/6] cpufreq/sched: Set need_freq_update in ignore_dl_rate_limit()

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Notice that ignore_dl_rate_limit() need not piggy back on the
limits_changed handling to achieve its goal (which is to enforce a
frequency update before its due time).

Namely, if sugov_should_update_freq() is updated to check
sg_policy->need_freq_update and return 'true' if it is set when
sg_policy->limits_changed is not set, ignore_dl_rate_limit() may
set the former directly instead of setting the latter, so it can
avoid hitting the memory barrier in sugov_should_update_freq().

Update the code accordingly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 kernel/sched/cpufreq_schedutil.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -96,6 +96,9 @@
 		smp_mb();

 		return true;
+	} else if (sg_policy->need_freq_update) {
+		/* ignore_dl_rate_limit() wants a new frequency to be found. */
+		return true;
 	}

 	delta_ns = time - sg_policy->last_freq_update_time;
@@ -388,7 +391,7 @@
 static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu)
 {
 	if (cpu_bw_dl(cpu_rq(sg_cpu->cpu)) > sg_cpu->bw_min)
-		WRITE_ONCE(sg_cpu->sg_policy->limits_changed, true);
+		sg_cpu->sg_policy->need_freq_update = true;
 }

 static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,