[RFC PATCH 04/10] arm: Frequency invariant scheduler load-tracking support

[Morten Rasmussen <morten.rasmussen@arm.com>]

From: Morten Rasmussen <Morten.Rasmussen@arm.com>

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

	current_freq(cpu) * SCHED_CAPACITY_SCALE / max_freq(cpu)

This implementation only provides frequency invariance. No
micro-architecture invariance yet.

Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 arch/arm/kernel/topology.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 89cfdd6..73ef337 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -169,6 +169,39 @@ static void update_cpu_capacity(unsigned int cpu)
 		cpu, arch_scale_cpu_capacity(NULL, cpu));
 }
 
+/*
+ * Scheduler load-tracking scale-invariance
+ *
+ * Provides the scheduler with a scale-invariance correction factor that
+ * compensates for frequency scaling.
+ */
+
+static DEFINE_PER_CPU(atomic_long_t, cpu_curr_freq);
+static DEFINE_PER_CPU(atomic_long_t, cpu_max_freq);
+
+/* cpufreq callback function setting current cpu frequency */
+void arch_scale_set_curr_freq(int cpu, unsigned long freq)
+{
+	atomic_long_set(&per_cpu(cpu_curr_freq, cpu), freq);
+}
+
+/* cpufreq callback function setting max cpu frequency */
+void arch_scale_set_max_freq(int cpu, unsigned long freq)
+{
+	atomic_long_set(&per_cpu(cpu_max_freq, cpu), freq);
+}
+
+unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
+{
+	unsigned long curr = atomic_long_read(&per_cpu(cpu_curr_freq, cpu));
+	unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu));
+
+	if (!max)
+		return SCHED_CAPACITY_SCALE;
+
+	return (curr * SCHED_CAPACITY_SCALE) / max;
+}
+
 #else
 static inline void parse_dt_topology(void) {}
 static inline void update_cpu_capacity(unsigned int cpuid) {}
-- 
1.9.1