linux-kernel - [PATCH 3/9] sched: Clean up DL server vs core sched

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Message-Id: <20240813224015.837303391@infradead.org>
Date: Wed, 14 Aug 2024 00:25:51 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...nel.org,
 tj@...nel.org,
 void@...ifault.com
Cc: peterz@...radead.org,
 juri.lelli@...hat.com,
 vincent.guittot@...aro.org,
 dietmar.eggemann@....com,
 rostedt@...dmis.org,
 bsegall@...gle.com,
 mgorman@...e.de,
 vschneid@...hat.com,
 linux-kernel@...r.kernel.org,
 joelaf@...gle.com
Subject: [PATCH 3/9] sched: Clean up DL server vs core sched

Abide by the simple rule:

  pick_next_task() := pick_task() + set_next_task(.first = true)

This allows us to trivially get rid of server_pick_next() and things
collapse nicely.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/linux/sched.h   |    1 -
 kernel/sched/deadline.c |   18 +++++++-----------
 kernel/sched/fair.c     |   13 +------------
 kernel/sched/sched.h    |    1 -
 4 files changed, 8 insertions(+), 25 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -692,7 +692,6 @@ struct sched_dl_entity {
 	 */
 	struct rq			*rq;
 	dl_server_has_tasks_f		server_has_tasks;
-	dl_server_pick_f		server_pick_next;
 	dl_server_pick_f		server_pick_task;
 
 #ifdef CONFIG_RT_MUTEXES
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1665,12 +1665,10 @@ void dl_server_stop(struct sched_dl_enti
 
 void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
 		    dl_server_has_tasks_f has_tasks,
-		    dl_server_pick_f pick_next,
 		    dl_server_pick_f pick_task)
 {
 	dl_se->rq = rq;
 	dl_se->server_has_tasks = has_tasks;
-	dl_se->server_pick_next = pick_next;
 	dl_se->server_pick_task = pick_task;
 }
 
@@ -2410,9 +2408,8 @@ static struct sched_dl_entity *pick_next
 /*
  * __pick_next_task_dl - Helper to pick the next -deadline task to run.
  * @rq: The runqueue to pick the next task from.
- * @peek: If true, just peek at the next task. Only relevant for dlserver.
  */
-static struct task_struct *__pick_next_task_dl(struct rq *rq, bool peek)
+static struct task_struct *__pick_task_dl(struct rq *rq)
 {
 	struct sched_dl_entity *dl_se;
 	struct dl_rq *dl_rq = &rq->dl;
@@ -2426,10 +2423,7 @@ static struct task_struct *__pick_next_t
 	WARN_ON_ONCE(!dl_se);
 
 	if (dl_server(dl_se)) {
-		if (IS_ENABLED(CONFIG_SMP) && peek)
-			p = dl_se->server_pick_task(dl_se);
-		else
-			p = dl_se->server_pick_next(dl_se);
+		p = dl_se->server_pick_task(dl_se);
 		if (!p) {
 			dl_se->dl_yielded = 1;
 			update_curr_dl_se(rq, dl_se, 0);
@@ -2446,7 +2440,7 @@ static struct task_struct *__pick_next_t
 #ifdef CONFIG_SMP
 static struct task_struct *pick_task_dl(struct rq *rq)
 {
-	return __pick_next_task_dl(rq, true);
+	return __pick_task_dl(rq);
 }
 #endif
 
@@ -2454,11 +2448,13 @@ static struct task_struct *pick_next_tas
 {
 	struct task_struct *p;
 
-	p = __pick_next_task_dl(rq, false);
+	p = __pick_task_dl(rq);
 	if (!p)
 		return p;
 
-	if (!p->dl_server)
+	if (p->dl_server)
+		p->sched_class->set_next_task(rq, p, true);
+	else
 		set_next_task_dl(rq, p, true);
 
 	return p;
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8860,16 +8860,7 @@ static bool fair_server_has_tasks(struct
 
 static struct task_struct *fair_server_pick_task(struct sched_dl_entity *dl_se)
 {
-#ifdef CONFIG_SMP
 	return pick_task_fair(dl_se->rq);
-#else
-	return NULL;
-#endif
-}
-
-static struct task_struct *fair_server_pick_next(struct sched_dl_entity *dl_se)
-{
-	return pick_next_task_fair(dl_se->rq, NULL, NULL);
 }
 
 void fair_server_init(struct rq *rq)
@@ -8878,9 +8869,7 @@ void fair_server_init(struct rq *rq)
 
 	init_dl_entity(dl_se);
 
-	dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick_next,
-		       fair_server_pick_task);
-
+	dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick_task);
 }
 
 /*
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -362,7 +362,6 @@ extern void dl_server_start(struct sched
 extern void dl_server_stop(struct sched_dl_entity *dl_se);
 extern void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
 		    dl_server_has_tasks_f has_tasks,
-		    dl_server_pick_f pick_next,
 		    dl_server_pick_f pick_task);
 
 extern void dl_server_update_idle_time(struct rq *rq,