[RFC 1/4] sched/core: Introduce per_cpu counter to track latency sensitive tasks

[Parth Shah <parth@linux.ibm.com>]

The "nr_lat_sensitive" per_cpu variable provides hints on the possible
number of latency-sensitive tasks occupying the CPU. This hints further
helps in inhibiting the CPUIDLE governor from calling deeper IDLE states
(next patches includes this).

Signed-off-by: Parth Shah <parth@linux.ibm.com>
---
 kernel/sched/core.c  | 2 ++
 kernel/sched/sched.h | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2576fd8cacf9..2d8b76f41d61 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6606,6 +6606,7 @@ static struct kmem_cache *task_group_cache __read_mostly;
 
 DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
 DECLARE_PER_CPU(cpumask_var_t, select_idle_mask);
+DEFINE_PER_CPU(int, nr_lat_sensitive);
 
 void __init sched_init(void)
 {
@@ -6737,6 +6738,7 @@ void __init sched_init(void)
 #endif /* CONFIG_SMP */
 		hrtick_rq_init(rq);
 		atomic_set(&rq->nr_iowait, 0);
+		per_cpu(nr_lat_sensitive, i) = 0;
 	}
 
 	set_load_weight(&init_task, false);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b2c86dfe913e..5c41020c530e 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1439,6 +1439,8 @@ DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
 DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
+DECLARE_PER_CPU(int, nr_lat_sensitive);
+
 extern struct static_key_false sched_asym_cpucapacity;
 
 struct sched_group_capacity {
-- 
2.17.2