[PATCH v3 3/6] cpufreq/schedutil: use a fixed reference frequency

[Vincent Guittot]

cpuinfo.max_freq can change at runtime because of boost as an example. This
implies that the value could be different 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 reference
frequency that can be used when computing a frequency based on utilization.

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

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Reviewed-by: Lukasz Luba <lukasz.luba@xxxxxxx>
Tested-by: Lukasz Luba <lukasz.luba@xxxxxxx>

---
 kernel/sched/cpufreq_schedutil.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 458d359f5991..6e4030482ae8 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -114,6 +114,28 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy)
 	}
 }
 
+/**
+ * cpufreq_get_capacity_ref_freq - get the reference frequency of a given CPU that
+ * has been used to correlate frequency and compute capacity.
+ * @policy: the cpufreq policy of the CPU in question.
+ * @use_current: Fallback to current freq instead of policy->cpuinfo.max_freq.
+ *
+ * Return: the reference CPU frequency to compute a capacity.
+ */
+static __always_inline
+unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy)
+{
+	unsigned int freq = arch_scale_freq_ref(policy->cpu);
+
+	if (freq)
+		return freq;
+
+	if (arch_scale_freq_invariant())
+		return policy->cpuinfo.max_freq;
+
+	return policy->cur;
+}
+
 /**
  * get_next_freq - Compute a new frequency for a given cpufreq policy.
  * @sg_policy: schedutil policy object to compute the new frequency for.
@@ -140,10 +162,10 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
 				  unsigned long util, unsigned long max)
 {
 	struct cpufreq_policy *policy = sg_policy->policy;
-	unsigned int freq = arch_scale_freq_invariant() ?
-				policy->cpuinfo.max_freq : policy->cur;
+	unsigned int freq;
 
 	util = map_util_perf(util);
+	freq = get_capacity_ref_freq(policy);
 	freq = map_util_freq(util, freq, max);
 
 	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
-- 
2.34.1