linux-kernel - [RFT][PATCH v1 2/8] cpufreq/sched: Move cpufreq-specific EAS checks to cpufreq

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Message-ID: <6039220.MhkbZ0Pkbq@rjwysocki.net>
Date: Wed, 16 Apr 2025 19:59:12 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Peter Zijlstra <peterz@...radead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Morten Rasmussen <morten.rasmussen@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
 Pierre Gondois <pierre.gondois@....com>,
 Christian Loehle <christian.loehle@....com>
Subject:
 [RFT][PATCH v1 2/8] cpufreq/sched: Move cpufreq-specific EAS checks to
 cpufreq

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

Doing cpufreq-specific EAS checks that require accessing policy
internals directly from sched_is_eas_possible() is a bit unfortunate,
so introduce cpufreq_ready_for_eas() in cpufreq, move those checks
into that new function and make sched_is_eas_possible() call it.

While at it, address a possible race between the EAS governor check
and governor change by doing the former under the policy rwsem.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---

v0.3 -> v1
     * Add a new helper called cpufreq_policy_is_good_for_eas() which is
       properly synchronized with governor changes.
     * Slightly modify debug messages.

This patch is regarded as a cleanup for 6.16.

---
 drivers/cpufreq/cpufreq.c |   32 ++++++++++++++++++++++++++++++++
 include/linux/cpufreq.h   |    2 ++
 kernel/sched/topology.c   |   25 +++++--------------------
 3 files changed, 39 insertions(+), 20 deletions(-)

--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -3041,6 +3041,38 @@
 
 	return 0;
 }
+
+static bool cpufreq_policy_is_good_for_eas(unsigned int cpu)
+{
+	struct cpufreq_policy *policy __free(put_cpufreq_policy);
+
+	policy = cpufreq_cpu_get(cpu);
+	if (!policy) {
+		pr_debug("cpufreq policy not set for CPU: %d", cpu);
+		return false;
+	}
+
+	guard(cpufreq_policy_read)(policy);
+
+	return sugov_is_governor(policy);
+}
+
+bool cpufreq_ready_for_eas(const struct cpumask *cpu_mask)
+{
+	unsigned int cpu;
+
+	/* Do not attempt EAS if schedutil is not being used. */
+	for_each_cpu(cpu, cpu_mask) {
+		if (!cpufreq_policy_is_good_for_eas(cpu)) {
+			pr_debug("rd %*pbl: schedutil is mandatory for EAS\n",
+				 cpumask_pr_args(cpu_mask));
+			return false;
+		}
+	}
+
+	return true;
+}
+
 module_param(off, int, 0444);
 module_param_string(default_governor, default_governor, CPUFREQ_NAME_LEN, 0444);
 core_initcall(cpufreq_core_init);
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -1212,6 +1212,8 @@
 		struct cpufreq_frequency_table *table,
 		unsigned int transition_latency);
 
+bool cpufreq_ready_for_eas(const struct cpumask *cpu_mask);
+
 static inline void cpufreq_register_em_with_opp(struct cpufreq_policy *policy)
 {
 	dev_pm_opp_of_register_em(get_cpu_device(policy->cpu),
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -212,8 +212,6 @@
 static bool sched_is_eas_possible(const struct cpumask *cpu_mask)
 {
 	bool any_asym_capacity = false;
-	struct cpufreq_policy *policy;
-	bool policy_is_ready;
 	int i;
 
 	/* EAS is enabled for asymmetric CPU capacity topologies. */
@@ -248,25 +246,12 @@
 		return false;
 	}
 
-	/* Do not attempt EAS if schedutil is not being used. */
-	for_each_cpu(i, cpu_mask) {
-		policy = cpufreq_cpu_get(i);
-		if (!policy) {
-			if (sched_debug()) {
-				pr_info("rd %*pbl: Checking EAS, cpufreq policy not set for CPU: %d",
-					cpumask_pr_args(cpu_mask), i);
-			}
-			return false;
-		}
-		policy_is_ready = sugov_is_governor(policy);
-		cpufreq_cpu_put(policy);
-		if (!policy_is_ready) {
-			if (sched_debug()) {
-				pr_info("rd %*pbl: Checking EAS, schedutil is mandatory\n",
-					cpumask_pr_args(cpu_mask));
-			}
-			return false;
+	if (!cpufreq_ready_for_eas(cpu_mask)) {
+		if (sched_debug()) {
+			pr_info("rd %*pbl: Checking EAS: cpufreq is not ready",
+				cpumask_pr_args(cpu_mask));
 		}
+		return false;
 	}
 
 	return true;