linux-kernel - [PATCH v1 09/10] cpufreq: Introduce cpufreq_policy

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Message-ID: <6047110.MhkbZ0Pkbq@rjwysocki.net>
Date: Fri, 28 Mar 2025 21:47:31 +0100
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>,
 Sudeep Holla <sudeep.holla@....com>
Subject: [PATCH v1 09/10] cpufreq: Introduce cpufreq_policy_refresh()

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

Since cpufreq_update_limits() obtains a cpufreq policy pointer for the
given CPU and reference counts the object pointed to by it, calling
cpufreq_update_policy() from cpufreq_update_limits() is somewhat
wasteful because that function calls cpufreq_cpu_get() on the same
CPU again.

To avoid that unnecessary overhead, move the part of the code running
under the policy rwsem from cpufreq_update_policy() to a new function
called cpufreq_policy_refresh() and invoke that new function from
both cpufreq_update_policy() and cpufreq_update_limits().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpufreq/cpufreq.c |   31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2689,6 +2689,21 @@
 	return ret;
 }

+static void cpufreq_policy_refresh(struct cpufreq_policy *policy)
+{
+	guard(cpufreq_policy_write)(policy);
+
+	/*
+	 * BIOS might change freq behind our back
+	 * -> ask driver for current freq and notify governors about a change
+	 */
+	if (cpufreq_driver->get && has_target() &&
+	    (cpufreq_suspended || WARN_ON(!cpufreq_verify_current_freq(policy, false))))
+		return;
+
+	refresh_frequency_limits(policy);
+}
+
 /**
  * cpufreq_update_policy - Re-evaluate an existing cpufreq policy.
  * @cpu: CPU to re-evaluate the policy for.
@@ -2706,17 +2721,7 @@
 	if (!policy)
 		return;

-	guard(cpufreq_policy_write)(policy);
-
-	/*
-	 * BIOS might change freq behind our back
-	 * -> ask driver for current freq and notify governors about a change
-	 */
-	if (cpufreq_driver->get && has_target() &&
-	    (cpufreq_suspended || WARN_ON(!cpufreq_verify_current_freq(policy, false))))
-		return;
-
-	refresh_frequency_limits(policy);
+	cpufreq_policy_refresh(policy);
 }
 EXPORT_SYMBOL(cpufreq_update_policy);

@@ -2725,7 +2730,7 @@
  * @cpu: CPU to update the policy limits for.
  *
  * Invoke the driver's ->update_limits callback if present or call
- * cpufreq_update_policy() for @cpu.
+ * cpufreq_policy_refresh() for @cpu.
  */
 void cpufreq_update_limits(unsigned int cpu)
 {
@@ -2738,7 +2743,7 @@
 	if (cpufreq_driver->update_limits)
 		cpufreq_driver->update_limits(cpu);
 	else
-		cpufreq_update_policy(cpu);
+		cpufreq_policy_refresh(policy);
 }
 EXPORT_SYMBOL_GPL(cpufreq_update_limits);