[RFCv3 PATCH 12/48] sched: Make usage tracking cpu scale-invariant

[Morten Rasmussen]

From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

Besides the existing frequency scale-invariance correction factor, apply
cpu scale-invariance correction factor to usage tracking.

Cpu scale-invariance takes cpu performance deviations due to
micro-architectural differences (i.e. instructions per seconds) between
cpus in HMP systems (e.g. big.LITTLE) and differences in the frequency
value of the highest OPP between cpus in SMP systems into consideration.

Each segment of the sched_avg::running_avg_sum geometric series is now
scaled by the cpu performance factor too so the
sched_avg::utilization_avg_contrib of each entity will be invariant from
the particular cpu of the HMP/SMP system it is gathered on.

So the usage level that is returned by get_cpu_usage stays relative to
the max cpu performance of the system.

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
---
 kernel/sched/fair.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e9a26b1..5375ab1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2473,6 +2473,7 @@ static u32 __compute_runnable_contrib(u64 n)
 }
 
 unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
+unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu);
 
 /*
  * We can represent the historical contribution to runnable average as the
@@ -2511,6 +2512,7 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
 	u32 runnable_contrib, scaled_runnable_contrib;
 	int delta_w, scaled_delta_w, decayed = 0;
 	unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
+	unsigned long scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
 
 	delta = now - sa->last_runnable_update;
 	/*
@@ -2547,6 +2549,10 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
 
 		if (runnable)
 			sa->runnable_avg_sum += scaled_delta_w;
+
+		scaled_delta_w *= scale_cpu;
+		scaled_delta_w >>= SCHED_CAPACITY_SHIFT;
+
 		if (running)
 			sa->running_avg_sum += scaled_delta_w;
 		sa->avg_period += delta_w;
@@ -2571,6 +2577,10 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
 
 		if (runnable)
 			sa->runnable_avg_sum += scaled_runnable_contrib;
+
+		scaled_runnable_contrib *= scale_cpu;
+		scaled_runnable_contrib >>= SCHED_CAPACITY_SHIFT;
+
 		if (running)
 			sa->running_avg_sum += scaled_runnable_contrib;
 		sa->avg_period += runnable_contrib;
@@ -2581,6 +2591,10 @@ static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
 
 	if (runnable)
 		sa->runnable_avg_sum += scaled_delta;
+
+	scaled_delta *= scale_cpu;
+	scaled_delta >>= SCHED_CAPACITY_SHIFT;
+
 	if (running)
 		sa->running_avg_sum += scaled_delta;
 	sa->avg_period += delta;
@@ -6014,7 +6028,7 @@ unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
 
 static unsigned long default_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 {
-	if ((sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
+	if (sd && (sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
 		return sd->smt_gain / sd->span_weight;
 
 	return SCHED_CAPACITY_SCALE;
-- 
1.9.1

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