[PATCH 1/4] cpufreq: Add a cpufreq pressure feedback for the scheduler

[Vincent Guittot]

Provide to the scheduler a feedback about the temporary max available
capacity. Unlike arch_update_thermal_pressure, this doesn't need to be
filtered as the pressure will happen for dozens ms or more.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
---
 drivers/cpufreq/cpufreq.c | 48 +++++++++++++++++++++++++++++++++++++++
 include/linux/cpufreq.h   | 10 ++++++++
 2 files changed, 58 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 44db4f59c4cc..7d5f71be8d29 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2563,6 +2563,50 @@ int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu)
 }
 EXPORT_SYMBOL(cpufreq_get_policy);
 
+DEFINE_PER_CPU(unsigned long, cpufreq_pressure);
+EXPORT_PER_CPU_SYMBOL_GPL(cpufreq_pressure);
+
+/**
+ * cpufreq_update_pressure() - Update cpufreq pressure for CPUs
+ * @cpus        : The related CPUs for which max capacity has been reduced
+ * @capped_freq : The maximum allowed frequency that CPUs can run at
+ *
+ * Update the value of cpufreq pressure for all @cpus in the mask. The
+ * cpumask should include all (online+offline) affected CPUs, to avoid
+ * operating on stale data when hot-plug is used for some CPUs. The
+ * @capped_freq reflects the currently allowed max CPUs frequency due to
+ * freq_qos capping. It might be also a boost frequency value, which is bigger
+ * than the internal 'capacity_freq_ref' max frequency. In such case the
+ * pressure value should simply be removed, since this is an indication that
+ * there is no capping. The @capped_freq must be provided in kHz.
+ */
+static void cpufreq_update_pressure(const struct cpumask *cpus,
+				      unsigned long capped_freq)
+{
+	unsigned long max_capacity, capacity, pressure;
+	u32 max_freq;
+	int cpu;
+
+	cpu = cpumask_first(cpus);
+	max_capacity = arch_scale_cpu_capacity(cpu);
+	max_freq = arch_scale_freq_ref(cpu);
+
+	/*
+	 * Handle properly the boost frequencies, which should simply clean
+	 * the thermal pressure value.
+	 */
+	if (max_freq <= capped_freq)
+		capacity = max_capacity;
+	else
+		capacity = mult_frac(max_capacity, capped_freq, max_freq);
+
+	pressure = max_capacity - capacity;
+
+
+	for_each_cpu(cpu, cpus)
+		WRITE_ONCE(per_cpu(cpufreq_pressure, cpu), pressure);
+}
+
 /**
  * cpufreq_set_policy - Modify cpufreq policy parameters.
  * @policy: Policy object to modify.
@@ -2584,6 +2628,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
 {
 	struct cpufreq_policy_data new_data;
 	struct cpufreq_governor *old_gov;
+	struct cpumask *cpus;
 	int ret;
 
 	memcpy(&new_data.cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo));
@@ -2618,6 +2663,9 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
 	policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
 	trace_cpu_frequency_limits(policy);
 
+	cpus = policy->related_cpus;
+	cpufreq_update_pressure(cpus, policy->max);
+
 	policy->cached_target_freq = UINT_MAX;
 
 	pr_debug("new min and max freqs are %u - %u kHz\n",
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index afda5f24d3dd..b1d97edd3253 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -241,6 +241,12 @@ struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
 void cpufreq_enable_fast_switch(struct cpufreq_policy *policy);
 void cpufreq_disable_fast_switch(struct cpufreq_policy *policy);
 bool has_target_index(void);
+
+DECLARE_PER_CPU(unsigned long, cpufreq_pressure);
+static inline unsigned long cpufreq_get_pressure(int cpu)
+{
+	return per_cpu(cpufreq_pressure, cpu);
+}
 #else
 static inline unsigned int cpufreq_get(unsigned int cpu)
 {
@@ -263,6 +269,10 @@ static inline bool cpufreq_supports_freq_invariance(void)
 	return false;
 }
 static inline void disable_cpufreq(void) { }
+static inline unsigned long cpufreq_get_pressure(int cpu)
+{
+	return 0;
+}
 #endif
 
 #ifdef CONFIG_CPU_FREQ_STAT
-- 
2.34.1