[PATCH 03/18 v2] sched/eevdf: Add per cpu cached min_slice

[Vincent Guittot]

In order to use min_slice during cpu selection, update a cached value when
needed after en/dequeing a new task. This cached value includes current
task.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
---
 kernel/sched/core.c  |  1 +
 kernel/sched/fair.c  | 20 ++++++++++++++++++++
 kernel/sched/sched.h |  1 +
 3 files changed, 22 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee9b443f760d..f38cf5a37a8a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8902,6 +8902,7 @@ void __init sched_init(void)
 		rq->sd = NULL;
 		rq->rd = NULL;
 		rq->cpu_capacity = SCHED_CAPACITY_SCALE;
+		rq->min_slice = ULONG_MAX;
 		rq->balance_callback = &balance_push_callback;
 		rq->active_balance = 0;
 		rq->next_balance = jiffies;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4c8f12fc8869..ad72b8536d6c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1116,6 +1116,22 @@ static inline bool min_vruntime_update(struct sched_entity *se, bool exit)
 RB_DECLARE_CALLBACKS(static, min_vruntime_cb, struct sched_entity,
 		     run_node, min_vruntime, min_vruntime_update);
 
+/*
+ * Entity's slice is in the range [100us:100ms].
+ */
+static unsigned long get_rq_min_slice(struct rq *rq)
+{
+	return READ_ONCE(rq->min_slice);
+}
+
+static void __update_rq_min_slice(struct rq *rq)
+{
+	unsigned long min = cfs_rq_min_slice(&rq->cfs);
+
+	if (min != get_rq_min_slice(rq))
+		WRITE_ONCE(rq->min_slice, min);
+}
+
 /*
  * Enqueue an entity into the rb-tree:
  */
@@ -8089,6 +8105,8 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	place_entity(cfs_rq, se, flags | ENQUEUE_QUEUED);
 	__enqueue_entity(cfs_rq, se);
 
+	__update_rq_min_slice(rq);
+
 	if (!rq_h_nr_queued && rq->cfs.h_nr_queued)
 		dl_server_start(&rq->fair_server);
 
@@ -8214,6 +8232,8 @@ static bool __dequeue_task(struct rq *rq, struct task_struct *p, int flags)
 	if (se != cfs_rq->curr)
 		__dequeue_entity(cfs_rq, se);
 
+	__update_rq_min_slice(rq);
+
 	sub_nr_running(rq, 1);
 
 	/* balance early to pull high priority tasks */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 69a2a749e188..e025d2a6c302 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1173,6 +1173,7 @@ struct rq {
 #endif
 	unsigned int		ttwu_pending;
 	unsigned long		cpu_capacity;
+	unsigned long		min_slice;
 #ifdef CONFIG_SCHED_PROXY_EXEC
 	struct task_struct __rcu	*donor;  /* Scheduling context */
 	struct task_struct __rcu	*curr;   /* Execution context */
-- 
2.53.0