linux-kernel - [PATCH 3/4] cpufreq/schedutil: use a fixed reference frequency

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Message-Id: <20230901130312.247719-4-vincent.guittot@linaro.org>
Date:   Fri,  1 Sep 2023 15:03:11 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, sudeep.holla@....com,
        gregkh@...uxfoundation.org, rafael@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        viresh.kumar@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-pm@...r.kernel.org
Cc:     conor.dooley@...rochip.com, suagrfillet@...il.com,
        ajones@...tanamicro.com, lftan@...nel.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 3/4] cpufreq/schedutil: use a fixed reference frequency

cpuinfo_max_freq can change at runtime because of boost as example. This
implies that the value could not be the same than the one that has been
used when computing the capacity of a CPU.

The new arch_scale_freq_ref() returns a fixed and coherent frequency
reference that can be used when computing a frequency based on utilization.

Use this arch_scale_freq_ref() when available and fallback to
cpuinfo.max_freq otherwise.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/cpufreq_schedutil.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 4492608b7d7f..9996ef429e2b 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -114,6 +114,31 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy)
 	}
 }
 
+#ifdef arch_scale_freq_ref
+/**
+ * arch_scale_freq_ref_policy - get the reference frequency of a given CPU that
+ * has been used to correlate frequency and compute capacity.
+ * @cpu: the CPU in question.
+ *
+ * Return: the reference CPU frequency.
+ */
+static __always_inline
+unsigned long  arch_scale_freq_ref_policy(struct cpufreq_policy *policy)
+{
+	return arch_scale_freq_ref(policy->cpu);
+}
+#else
+static __always_inline
+unsigned long  arch_scale_freq_ref_policy(struct cpufreq_policy *policy)
+{
+	if (arch_scale_freq_invariant())
+		return policy->cpuinfo.max_freq;
+
+
+	return policy->cur;
+}
+#endif
+
 /**
  * get_next_freq - Compute a new frequency for a given cpufreq policy.
  * @sg_policy: schedutil policy object to compute the new frequency for.
@@ -139,11 +164,11 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy)
 static unsigned int get_next_freq(struct sugov_policy *sg_policy,
 				  unsigned long util, unsigned long max)
 {
+	unsigned int freq;
 	struct cpufreq_policy *policy = sg_policy->policy;
-	unsigned int freq = arch_scale_freq_invariant() ?
-				policy->cpuinfo.max_freq : policy->cur;
 
 	util = map_util_perf(util);
+	freq = arch_scale_freq_ref_policy(policy);
 	freq = map_util_freq(util, freq, max);
 
 	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
-- 
2.34.1