linux-kernel - [PATCH 1/1] cpufreq: Rewire arch specific feedback for cpuinfo/scaling_cur

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Date: Mon,  3 Jun 2024 09:13:31 +0100
From: Beata Michalska <beata.michalska@....com>
To: linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	rafael@...nel.org,
	viresh.kumar@...aro.org,
	len.brown@...el.com
Cc: ionela.voinescu@....com,
	vanshikonda@...amperecomputing.com,
	sumitg@...dia.com
Subject: [PATCH 1/1] cpufreq: Rewire arch specific feedback for cpuinfo/scaling_cur_freq

Some architectures provide a way to determine an average frequency over
a certain period of time, based on available performance monitors (AMU on
ARM or APERF/MPERf on x86). With those at hand, enroll arch_freq_get_on_cpu
into cpuinfo_cur_freq policy sysfs attribute handler, which is expected to
represent the current frequency of a given CPU,as obtained by the hardware.
This is the type of feedback that counters do provide.
At the same time, keep the scaling_cur_freq attribute align with the docs
and make it provide most recently requested frequency, still allowing to
fallback to using arch_freq_get_on_cpu for cases when cpuinfo_cur_freq is
not available.

Signed-off-by: Beata Michalska <beata.michalska@....com>
---
 drivers/cpufreq/cpufreq.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index a45aac17c20f..3b0eabe4a983 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -758,7 +758,8 @@ static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
 	ssize_t ret;
 	unsigned int freq;

-	freq = arch_freq_get_on_cpu(policy->cpu);
+	freq = !cpufreq_driver->get ? arch_freq_get_on_cpu(policy->cpu)
+				    : 0;
 	if (freq)
 		ret = sprintf(buf, "%u\n", freq);
 	else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
@@ -795,7 +796,10 @@ store_one(scaling_max_freq, max);
 static ssize_t show_cpuinfo_cur_freq(struct cpufreq_policy *policy,
 					char *buf)
 {
-	unsigned int cur_freq = __cpufreq_get(policy);
+	unsigned int cur_freq = arch_freq_get_on_cpu(policy->cpu);
+
+	if (!cur_freq)
+		cur_freq = __cpufreq_get(policy);

 	if (cur_freq)
 		return sprintf(buf, "%u\n", cur_freq);
-- 
2.25.1