[RFC PATCH 1/3] sched/core: Track the core-wide pick leader

[K Prateek Nayak]

Track the rq whose task is dictating the core-wide cookie. If no
core-cookie is set (!needs_sync), every rq on the core is considered a
pick leader as it can individually try to dictate a core cookie later.

This detail will be used in subsequent commits to extend proxy execution
to remain compatible with core scheduling.

No functional changes intended.

Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
---
 kernel/sched/core.c  | 11 +++++++++--
 kernel/sched/sched.h |  3 +++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 25851bb5489d..31fa6bcee616 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6649,9 +6649,9 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
 	const struct cpumask *smt_mask;
 	bool fi_before = false;
 	bool core_clock_updated = (rq == rq->core);
+	struct rq *rq_i, *rq_max;
 	unsigned long cookie;
 	int i, cpu, occ = 0;
-	struct rq *rq_i;
 	bool need_sync;
 
 	if (!sched_core_enabled(rq))
@@ -6668,6 +6668,7 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
 		 */
 		rq->core_pick = NULL;
 		rq->core_dl_server = NULL;
+		rq->core_pick_leader = true;
 		return __pick_next_task(rq, rf);
 	}
 
@@ -6737,6 +6738,7 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
 		if (!next->core_cookie) {
 			rq->core_pick = NULL;
 			rq->core_dl_server = NULL;
+			rq->core_pick_leader = true;
 			/*
 			 * For robustness, update the min_vruntime_fi for
 			 * unconstrained picks as well.
@@ -6755,6 +6757,7 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
 	 */
 restart_multi:
 	max = NULL;
+	rq_max = NULL;
 	for_each_cpu_wrap(i, smt_mask, cpu) {
 		rq_i = cpu_rq(i);
 
@@ -6772,11 +6775,15 @@ pick_next_task(struct rq *rq, struct rq_flags *rf)
 
 		rq_i->core_pick = p;
 		rq_i->core_dl_server = rq_i->dl_server;
+		rq_i->core_pick_leader = false;
 
-		if (!max || prio_less(max, p, fi_before))
+		if (!max || prio_less(max, p, fi_before)) {
 			max = p;
+			rq_max = rq_i;
+		}
 	}
 
+	rq_max->core_pick_leader = true;
 	cookie = rq->core->core_cookie = max->core_cookie;
 
 	/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9539867e9e0f..b80a5eb384f0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1350,6 +1350,9 @@ struct rq {
 	unsigned int		core_sched_seq;
 	struct rb_root		core_tree;
 
+	/* private state for sched_proxy_exec()  */
+	bool			core_pick_leader;
+
 	/* shared state -- careful with sched_core_cpu_deactivate() */
 	unsigned int		core_task_seq;
 	unsigned int		core_pick_seq;
-- 
2.43.0