[PATCH 2/6] drivers base/arch_topology: frequency-invariant load-tracking support

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

Implements an arch-specific frequency-scaling function
topology_get_freq_scale() which provides the following frequency
scaling factor:

  current_freq(cpu) << SCHED_CAPACITY_SHIFT / max_supported_freq(cpu)

The debug output in init_cpu_capacity_callback() has been changed to be
able to distinguish whether cpu capacity and max frequency or only max
frequency has been set. The latter case happens on systems where there
is no or broken cpu capacity binding (cpu node property
capacity-dmips-mhz) information.

One possible consumer of this is the Per-Entity Load Tracking (PELT)
mechanism of the task scheduler.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---
 drivers/base/arch_topology.c  | 52 ++++++++++++++++++++++++++++++++++++++++---
 include/linux/arch_topology.h |  2 ++
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 272831c89feb..f6f14670bdab 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -24,12 +24,18 @@
 
 static DEFINE_MUTEX(cpu_scale_mutex);
 static DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
+static DEFINE_PER_CPU(unsigned long, freq_scale) = SCHED_CAPACITY_SCALE;
 
 unsigned long topology_get_cpu_scale(struct sched_domain *sd, int cpu)
 {
 	return per_cpu(cpu_scale, cpu);
 }
 
+unsigned long topology_get_freq_scale(struct sched_domain *sd, int cpu)
+{
+	return per_cpu(freq_scale, cpu);
+}
+
 void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
 {
 	per_cpu(cpu_scale, cpu) = capacity;
@@ -164,6 +170,7 @@ static cpumask_var_t cpus_to_visit;
 static bool cap_parsing_done;
 static void parsing_done_workfn(struct work_struct *work);
 static DECLARE_WORK(parsing_done_work, parsing_done_workfn);
+static DEFINE_PER_CPU(unsigned long, max_freq);
 
 static int
 init_cpu_capacity_callback(struct notifier_block *nb,
@@ -185,6 +192,7 @@ init_cpu_capacity_callback(struct notifier_block *nb,
 			       cpus_to_visit,
 			       policy->related_cpus);
 		for_each_cpu(cpu, policy->related_cpus) {
+			per_cpu(max_freq, cpu) = policy->cpuinfo.max_freq;
 			if (cap_parsing_failed)
 				continue;
 			raw_capacity[cpu] = topology_get_cpu_scale(NULL, cpu) *
@@ -195,8 +203,10 @@ init_cpu_capacity_callback(struct notifier_block *nb,
 			if (!cap_parsing_failed) {
 				topology_normalize_cpu_scale();
 				kfree(raw_capacity);
+				pr_debug("cpu_capacity: parsing done\n");
+			} else {
+				pr_debug("cpu_capacity: max frequency parsing done\n");
 			}
-			pr_debug("cpu_capacity: parsing done\n");
 			cap_parsing_done = true;
 			schedule_work(&parsing_done_work);
 		}
@@ -208,8 +218,38 @@ static struct notifier_block init_cpu_capacity_notifier = {
 	.notifier_call = init_cpu_capacity_callback,
 };
 
+static void set_freq_scale(unsigned int cpu, unsigned long freq)
+{
+	unsigned long max = per_cpu(max_freq, cpu);
+
+	if (!max)
+		return;
+
+	per_cpu(freq_scale, cpu) = (freq << SCHED_CAPACITY_SHIFT) / max;
+}
+
+static int set_freq_scale_callback(struct notifier_block *nb,
+				   unsigned long val,
+				   void *data)
+{
+	struct cpufreq_freqs *freq = data;
+
+	switch (val) {
+	case CPUFREQ_PRECHANGE:
+		set_freq_scale(freq->cpu, freq->new);
+	}
+
+	return 0;
+}
+
+static struct notifier_block set_freq_scale_notifier = {
+	.notifier_call = set_freq_scale_callback,
+};
+
 static int __init register_cpufreq_notifier(void)
 {
+	int ret;
+
 	/*
 	 * on ACPI-based systems we need to use the default cpu capacity
 	 * until we have the necessary code to parse the cpu capacity, so
@@ -225,8 +265,14 @@ static int __init register_cpufreq_notifier(void)
 
 	cpumask_copy(cpus_to_visit, cpu_possible_mask);
 
-	return cpufreq_register_notifier(&init_cpu_capacity_notifier,
-					 CPUFREQ_POLICY_NOTIFIER);
+	ret = cpufreq_register_notifier(&init_cpu_capacity_notifier,
+					CPUFREQ_POLICY_NOTIFIER);
+
+	if (ret)
+		return ret;
+
+	return cpufreq_register_notifier(&set_freq_scale_notifier,
+					 CPUFREQ_TRANSITION_NOTIFIER);
 }
 core_initcall(register_cpufreq_notifier);
 
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index 9af3c174c03a..3fb4d8ccb179 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -12,6 +12,8 @@ int topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu);
 struct sched_domain;
 unsigned long topology_get_cpu_scale(struct sched_domain *sd, int cpu);
 
+unsigned long topology_get_freq_scale(struct sched_domain *sd, int cpu);
+
 void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity);
 
 #endif /* _LINUX_ARCH_TOPOLOGY_H_ */
-- 
2.11.0