[RFC PATCH 02/16] sched/core: Use enqueue/dequeue flags instead of task_on_rq_migrating()

[K Prateek Nayak]

With the blocked task activation path converted to use a separate
helper, add the DEQUEUE_MIGRATING and ENQUEUE_MIGRATING flag in
deactivate_task() and activate_task().

Avoid checking task_on_rq_migrating() in the sched class callbacks and
instead depend on flags to know if the enqueue/dequeue is a part of a
task migration.

No functional changes intended.

Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
---
 kernel/sched/core.c     | 7 ++-----
 kernel/sched/deadline.c | 6 ------
 kernel/sched/fair.c     | 6 +++---
 kernel/sched/stats.h    | 2 +-
 4 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7d1ffcc33fed..4cd69b08b415 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2218,9 +2218,6 @@ inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
 
 static void __activate_task(struct rq *rq, struct task_struct *p, int flags)
 {
-	if (task_on_rq_migrating(p))
-		flags |= ENQUEUE_MIGRATED;
-
 	enqueue_task(rq, p, flags);
 
 	WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
@@ -2229,7 +2226,7 @@ static void __activate_task(struct rq *rq, struct task_struct *p, int flags)
 
 void activate_task(struct rq *rq, struct task_struct *p, int en_flags)
 {
-	__activate_task(rq, p, en_flags);
+	__activate_task(rq, p, en_flags | ENQUEUE_MIGRATING);
 }
 
 static void activate_blocked_task(struct rq *rq, struct task_struct *p, int en_flags)
@@ -2249,7 +2246,7 @@ void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 	 * dequeue_task() and cleared *after* enqueue_task().
 	 */
 
-	dequeue_task(rq, p, flags);
+	dequeue_task(rq, p, flags | DEQUEUE_MIGRATING);
 }
 
 static void block_task(struct rq *rq, struct task_struct *p, unsigned long task_state)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 3e89b3abeb27..9abda560c633 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2530,9 +2530,6 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 	check_schedstat_required();
 	update_stats_wait_start_dl(dl_rq, dl_se);
 
-	if (task_on_rq_migrating(p))
-		flags |= ENQUEUE_MIGRATING;
-
 	enqueue_dl_entity(dl_se, flags);
 
 	if (dl_server(dl_se))
@@ -2552,9 +2549,6 @@ static bool dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 {
 	update_curr_dl(rq);
 
-	if (task_on_rq_migrating(p))
-		flags |= DEQUEUE_MIGRATING;
-
 	dequeue_dl_entity(&p->dl, flags);
 	if (!p->dl.dl_throttled && !dl_server(&p->dl))
 		dequeue_pushable_dl_task(rq, p);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6d2fa0cd7777..244f1c68c041 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6265,7 +6265,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 
 	action = UPDATE_TG;
 	if (entity_is_task(se)) {
-		if (task_on_rq_migrating(task_of(se)))
+		if (flags & DEQUEUE_MIGRATING)
 			action |= DO_DETACH;
 
 		if (sleep && !(flags & DEQUEUE_DELAYED))
@@ -6663,7 +6663,7 @@ static void dequeue_throttled_task(struct task_struct *p, int flags)
 	 * task is migrating off its old cfs_rq, detach
 	 * the task's load from its old cfs_rq.
 	 */
-	if (task_on_rq_migrating(p))
+	if (flags & DEQUEUE_MIGRATING)
 		detach_task_cfs_rq(p);
 }
 
@@ -7981,7 +7981,7 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
 			break;
 		}
 		flags |= DEQUEUE_SLEEP;
-		flags &= ~(DEQUEUE_DELAYED | DEQUEUE_SPECIAL);
+		flags &= ~(DEQUEUE_DELAYED | DEQUEUE_SPECIAL | DEQUEUE_MIGRATING);
 	}
 
 	for_each_sched_entity(se) {
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index ebe0a7765f98..d0d9cff168a2 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -137,7 +137,7 @@ static inline void psi_enqueue(struct task_struct *p, int flags)
 
 	if (p->se.sched_delayed) {
 		/* CPU migration of "sleeping" task */
-		WARN_ON_ONCE(!(flags & ENQUEUE_MIGRATED));
+		WARN_ON_ONCE(!(flags & ENQUEUE_MIGRATING));
 		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
 		if (p->in_iowait)
-- 
2.34.1