sched: add per rq cpu_capacity_orig

This new field cpu_capacity_orig reflects the original capacity of a CPU
before being altered by rt tasks and/or IRQ

The cpu_capacity_orig will be used:
- to detect when the capacity of a CPU has been noticeably reduced so we can
  trig load balance to look for a CPU with better capacity. As an example, we
  can detect when a CPU handles a significant amount of irq
  (with CONFIG_IRQ_TIME_ACCOUNTING) but this CPU is seen as an idle CPU by
  scheduler whereas CPUs, which are really idle, are available.
- evaluate the available capacity for CFS tasks

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b37c27b18839..47827334a2a5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4141,6 +4141,11 @@ static unsigned long capacity_of(int cpu)
 	return cpu_rq(cpu)->cpu_capacity;
 }
 
+static unsigned long capacity_orig_of(int cpu)
+{
+	return cpu_rq(cpu)->cpu_capacity_orig;
+}
+
 static unsigned long cpu_avg_load_per_task(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
@@ -5821,6 +5826,7 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
 
 	capacity >>= SCHED_CAPACITY_SHIFT;
 
+	cpu_rq(cpu)->cpu_capacity_orig = capacity;
 	sdg->sgc->capacity_orig = capacity;
 
 	capacity *= scale_rt_capacity(cpu);
@@ -5875,7 +5881,7 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
 			 * Runtime updates will correct capacity_orig.
 			 */
 			if (unlikely(!rq->sd)) {
-				capacity_orig += capacity_of(cpu);
+				capacity_orig += capacity_orig_of(cpu);
 				capacity += capacity_of(cpu);
 				continue;
 			}