From 1be4a1e126cdb1b47b4d8a5dd156f8bca04715c0 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Fri, 3 Jul 2015 10:02:53 +0200
Subject: [PATCH] arm64: Frequency invariant scheduler load-tracking support

Implements arch-specific function to provide the scheduler with a
frequency scaling correction factor for more accurate load-tracking.

This patch is based on the implementation that has been done for arm arch
by Morten Rasmussen <morten.rasmussen@arm.com>

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 arch/arm64/include/asm/topology.h | 11 ++++++
 arch/arm64/kernel/smp.c           | 80 +++++++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/topology.c      | 19 ++++++++++
 3 files changed, 110 insertions(+)

diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
index 7ebcd31..887835a 100644
--- a/arch/arm64/include/asm/topology.h
+++ b/arch/arm64/include/asm/topology.h
@@ -24,6 +24,17 @@ void init_cpu_topology(void);
 void store_cpu_topology(unsigned int cpuid);
 const struct cpumask *cpu_coregroup_mask(int cpu);
 
+#ifdef CONFIG_CPU_FREQ
+
+#define arch_scale_freq_capacity arm64_arch_scale_freq_capacity
+struct sched_domain;
+extern unsigned long arm64_arch_scale_freq_capacity(struct sched_domain *sd,
+				int cpu);
+
+DECLARE_PER_CPU(atomic_long_t, cpu_freq_capacity);
+
+#endif /* CONFIG_CPU_FREQ */
+
 #else
 
 static inline void init_cpu_topology(void) { }
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 328b8ce..45b88cb 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -34,6 +34,7 @@
 #include <linux/percpu.h>
 #include <linux/clockchips.h>
 #include <linux/completion.h>
+#include <linux/cpufreq.h>
 #include <linux/of.h>
 #include <linux/irq_work.h>
 
@@ -656,3 +657,82 @@ int setup_profiling_timer(unsigned int multiplier)
 {
 	return -EINVAL;
 }
+
+#ifdef CONFIG_CPU_FREQ
+
+static DEFINE_PER_CPU(atomic_long_t, cpu_max_freq);
+DEFINE_PER_CPU(atomic_long_t, cpu_freq_capacity);
+
+/*
+ * Scheduler load-tracking scale-invariance
+ *
+ * Provides the scheduler with a scale-invariance correction factor that
+ * compensates for frequency scaling through arch_scale_freq_capacity()
+ * (implemented in topology.c).
+ */
+static inline
+void scale_freq_capacity(int cpu, unsigned long curr, unsigned long max)
+{
+	unsigned long capacity;
+
+	if (!max)
+		return;
+
+	capacity = (curr << SCHED_CAPACITY_SHIFT) / max;
+	atomic_long_set(&per_cpu(cpu_freq_capacity, cpu), capacity);
+}
+
+static int cpufreq_callback(struct notifier_block *nb,
+					unsigned long val, void *data)
+{
+	struct cpufreq_freqs *freq = data;
+	int cpu = freq->cpu;
+	unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu));
+
+	if (freq->flags & CPUFREQ_CONST_LOOPS)
+		return NOTIFY_OK;
+
+	scale_freq_capacity(cpu, freq->new, max);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block cpufreq_notifier = {
+	.notifier_call  = cpufreq_callback,
+};
+
+static int cpufreq_policy_callback(struct notifier_block *nb,
+						unsigned long val, void *data)
+{
+	struct cpufreq_policy *policy = data;
+	int i;
+
+	if (val != CPUFREQ_NOTIFY)
+		return NOTIFY_OK;
+
+	for_each_cpu(i, policy->cpus) {
+		scale_freq_capacity(i, policy->cur, policy->max);
+		atomic_long_set(&per_cpu(cpu_max_freq, i), policy->max);
+	}
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block cpufreq_policy_notifier = {
+	.notifier_call	= cpufreq_policy_callback,
+};
+
+static int __init register_cpufreq_notifier(void)
+{
+	int ret;
+
+	ret = cpufreq_register_notifier(&cpufreq_notifier,
+						CPUFREQ_TRANSITION_NOTIFIER);
+	if (ret)
+		return ret;
+
+	return cpufreq_register_notifier(&cpufreq_policy_notifier,
+						CPUFREQ_POLICY_NOTIFIER);
+}
+core_initcall(register_cpufreq_notifier);
+#endif
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index fcb8f7b..6387f65 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -200,6 +200,25 @@ static int __init parse_dt_topology(void)
 	return ret;
 }
 
+#ifdef CONFIG_CPU_FREQ
+/*
+ * Scheduler load-tracking scale-invariance
+ *
+ * Provides the scheduler with a scale-invariance correction factor that
+ * compensates for frequency scaling (arch_scale_freq_capacity()). The scaling
+ * factor is updated in smp.c
+ */
+unsigned long arm64_arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
+{
+	unsigned long curr = atomic_long_read(&per_cpu(cpu_freq_capacity, cpu));
+
+	if (!curr)
+		return SCHED_CAPACITY_SCALE;
+
+	return curr;
+}
+#endif
+
 /*
  * cpu topology table
  */
-- 
1.9.1

