Merge branch 'tip/sched/core' into for-6.12

- Resolve trivial context conflicts from dl_server clearing being moved
  around.

- Add @next to put_prev_task_scx() and @prev to pick_next_task_scx() to
  match sched/core.

- Merge sched_class->switch_class() addition from sched_ext with
  tip/sched/core changes in __pick_next_task().

- Make pick_next_task_scx() call put_prev_task_scx() to emulate the previous
  behavior where sched_class->put_prev_task() was called before
  sched_class->pick_next_task().

While this makes sched_ext build and function, the behavior is not in line
with other sched classes. The follow-up patches will address the
discrepancies and remove sched_class->switch_class().

Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/sched.h

@@ -694,7 +694,6 @@ 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

kernel/sched/core.c

@@ -3690,8 +3690,6 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
 		rq->idle_stamp = 0;
 	}
 #endif
-
-	p->dl_server = NULL;
 }
 
 /*
@@ -5895,7 +5893,7 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
 	schedstat_inc(this_rq()->sched_count);
 }
 
-static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
+static void prev_balance(struct rq *rq, struct task_struct *prev,
 			 struct rq_flags *rf)
 {
 	const struct sched_class *start_class = prev->sched_class;
@@ -5923,16 +5921,6 @@ static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
 		if (class->balance && class->balance(rq, prev, rf))
 			break;
 	}
-
-	put_prev_task(rq, prev);
-
-	/*
-	 * We've updated @prev and no longer need the server link, clear it.
-	 * Must be done before ->pick_next_task() because that can (re)set
-	 * ->dl_server.
-	 */
-	if (prev->dl_server)
-		prev->dl_server = NULL;
 }
 
 /*
@@ -5944,6 +5932,8 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 	const struct sched_class *class;
 	struct task_struct *p;
 
+	rq->dl_server = NULL;
+
 	if (scx_enabled())
 		goto restart;
 
@@ -5962,32 +5952,19 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 
 		/* Assume the next prioritized class is idle_sched_class */
 		if (!p) {
-			put_prev_task(rq, prev);
+			p = pick_task_idle(rq);
-			p = pick_next_task_idle(rq);
+			put_prev_set_next_task(rq, prev, p);
 		}
 
-		/*
-		 * This is a normal CFS pick, but the previous could be a DL pick.
-		 * Clear it as previous is no longer picked.
-		 */
-		if (prev->dl_server)
-			prev->dl_server = NULL;
-
-		/*
-		 * This is the fast path; it cannot be a DL server pick;
-		 * therefore even if @p == @prev, ->dl_server must be NULL.
-		 */
-		if (p->dl_server)
-			p->dl_server = NULL;
-
 		return p;
 	}
 
 restart:
-	put_prev_task_balance(rq, prev, rf);
+	prev_balance(rq, prev, rf);
 
 	for_each_active_class(class) {
-		p = class->pick_next_task(rq);
+		if (class->pick_next_task) {
+			p = class->pick_next_task(rq, prev);
 			if (p) {
 				const struct sched_class *prev_class = prev->sched_class;
 
@@ -5995,6 +5972,18 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 					prev_class->switch_class(rq, p);
 				return p;
 			}
+		} else {
+			p = class->pick_task(rq);
+			if (p) {
+				const struct sched_class *prev_class = prev->sched_class;
+
+				put_prev_set_next_task(rq, prev, p);
+
+				if (class != prev_class && prev_class->switch_class)
+					prev_class->switch_class(rq, p);
+				return p;
+			}
+		}
 	}
 
 	BUG(); /* The idle class should always have a runnable task. */
@@ -6024,6 +6013,8 @@ static inline struct task_struct *pick_task(struct rq *rq)
 	const struct sched_class *class;
 	struct task_struct *p;
 
+	rq->dl_server = NULL;
+
 	for_each_active_class(class) {
 		p = class->pick_task(rq);
 		if (p)
@@ -6062,6 +6053,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		 * another cpu during offline.
 		 */
 		rq->core_pick = NULL;
+		rq->core_dl_server = NULL;
 		return __pick_next_task(rq, prev, rf);
 	}
 
@@ -6080,16 +6072,13 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		WRITE_ONCE(rq->core_sched_seq, rq->core->core_pick_seq);
 
 		next = rq->core_pick;
-		if (next != prev) {
+		rq->dl_server = rq->core_dl_server;
-			put_prev_task(rq, prev);
-			set_next_task(rq, next);
-		}
-
 		rq->core_pick = NULL;
-		goto out;
+		rq->core_dl_server = NULL;
+		goto out_set_next;
 	}
 
-	put_prev_task_balance(rq, prev, rf);
+	prev_balance(rq, prev, rf);
 
 	smt_mask = cpu_smt_mask(cpu);
 	need_sync = !!rq->core->core_cookie;
@@ -6130,6 +6119,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		next = pick_task(rq);
 		if (!next->core_cookie) {
 			rq->core_pick = NULL;
+			rq->core_dl_server = NULL;
 			/*
 			 * For robustness, update the min_vruntime_fi for
 			 * unconstrained picks as well.
@@ -6157,7 +6147,9 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		if (i != cpu && (rq_i != rq->core || !core_clock_updated))
 			update_rq_clock(rq_i);
 
-		p = rq_i->core_pick = pick_task(rq_i);
+		rq_i->core_pick = p = pick_task(rq_i);
+		rq_i->core_dl_server = rq_i->dl_server;
+
 		if (!max || prio_less(max, p, fi_before))
 			max = p;
 	}
@@ -6181,6 +6173,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 		}
 
 		rq_i->core_pick = p;
+		rq_i->core_dl_server = NULL;
 
 		if (p == rq_i->idle) {
 			if (rq_i->nr_running) {
@@ -6241,6 +6234,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 
 		if (i == cpu) {
 			rq_i->core_pick = NULL;
+			rq_i->core_dl_server = NULL;
 			continue;
 		}
 
@@ -6249,6 +6243,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 
 		if (rq_i->curr == rq_i->core_pick) {
 			rq_i->core_pick = NULL;
+			rq_i->core_dl_server = NULL;
 			continue;
 		}
 
@@ -6256,8 +6251,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 	}
 
 out_set_next:
-	set_next_task(rq, next);
+	put_prev_set_next_task(rq, prev, next);
-out:
 	if (rq->core->core_forceidle_count && next == rq->idle)
 		queue_core_balance(rq);
 
@@ -8487,6 +8481,7 @@ void __init sched_init(void)
 #ifdef CONFIG_SCHED_CORE
 		rq->core = rq;
 		rq->core_pick = NULL;
+		rq->core_dl_server = NULL;
 		rq->core_enabled = 0;
 		rq->core_tree = RB_ROOT;
 		rq->core_forceidle_count = 0;

kernel/sched/deadline.c

@@ -1665,12 +1665,10 @@ void dl_server_stop(struct sched_dl_entity *dl_se)
 
 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;
 }
 
@@ -1896,45 +1894,39 @@ static inline bool __dl_less(struct rb_node *a, const struct rb_node *b)
 	return dl_time_before(__node_2_dle(a)->deadline, __node_2_dle(b)->deadline);
 }
 
-static inline struct sched_statistics *
+static __always_inline struct sched_statistics *
 __schedstats_from_dl_se(struct sched_dl_entity *dl_se)
 {
+	if (!schedstat_enabled())
+		return NULL;
+
+	if (dl_server(dl_se))
+		return NULL;
+
 	return &dl_task_of(dl_se)->stats;
 }
 
 static inline void
 update_stats_wait_start_dl(struct dl_rq *dl_rq, struct sched_dl_entity *dl_se)
 {
-	struct sched_statistics *stats;
+	struct sched_statistics *stats = __schedstats_from_dl_se(dl_se);
-
+	if (stats)
-	if (!schedstat_enabled())
-		return;
-
-	stats = __schedstats_from_dl_se(dl_se);
 		__update_stats_wait_start(rq_of_dl_rq(dl_rq), dl_task_of(dl_se), stats);
 }
 
 static inline void
 update_stats_wait_end_dl(struct dl_rq *dl_rq, struct sched_dl_entity *dl_se)
 {
-	struct sched_statistics *stats;
+	struct sched_statistics *stats = __schedstats_from_dl_se(dl_se);
-
+	if (stats)
-	if (!schedstat_enabled())
-		return;
-
-	stats = __schedstats_from_dl_se(dl_se);
 		__update_stats_wait_end(rq_of_dl_rq(dl_rq), dl_task_of(dl_se), stats);
 }
 
 static inline void
 update_stats_enqueue_sleeper_dl(struct dl_rq *dl_rq, struct sched_dl_entity *dl_se)
 {
-	struct sched_statistics *stats;
+	struct sched_statistics *stats = __schedstats_from_dl_se(dl_se);
-
+	if (stats)
-	if (!schedstat_enabled())
-		return;
-
-	stats = __schedstats_from_dl_se(dl_se);
 		__update_stats_enqueue_sleeper(rq_of_dl_rq(dl_rq), dl_task_of(dl_se), stats);
 }
 
@@ -2392,6 +2384,9 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
 		update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);
 
 	deadline_queue_push_tasks(rq);
+
+	if (hrtick_enabled(rq))
+		start_hrtick_dl(rq, &p->dl);
 }
 
 static struct sched_dl_entity *pick_next_dl_entity(struct dl_rq *dl_rq)
@@ -2407,9 +2402,8 @@ static struct sched_dl_entity *pick_next_dl_entity(struct dl_rq *dl_rq)
 /*
  * __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;
@@ -2423,16 +2417,13 @@ static struct task_struct *__pick_next_task_dl(struct rq *rq, bool peek)
 	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);
 		if (!p) {
 			dl_se->dl_yielded = 1;
 			update_curr_dl_se(rq, dl_se, 0);
 			goto again;
 		}
-		p->dl_server = dl_se;
+		rq->dl_server = dl_se;
 	} else {
 		p = dl_task_of(dl_se);
 	}
@@ -2440,31 +2431,12 @@ static struct task_struct *__pick_next_task_dl(struct rq *rq, bool peek)
 	return p;
 }
 
-#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
-
-static struct task_struct *pick_next_task_dl(struct rq *rq)
-{
-	struct task_struct *p;
-
-	p = __pick_next_task_dl(rq, false);
-	if (!p)
-		return p;
-
-	if (!p->dl_server)
-		set_next_task_dl(rq, p, true);
-
-	if (hrtick_enabled(rq))
-		start_hrtick_dl(rq, &p->dl);
-
-	return p;
 }
 
-static void put_prev_task_dl(struct rq *rq, struct task_struct *p)
+static void put_prev_task_dl(struct rq *rq, struct task_struct *p, struct task_struct *next)
 {
 	struct sched_dl_entity *dl_se = &p->dl;
 	struct dl_rq *dl_rq = &rq->dl;
@@ -3156,13 +3128,12 @@ DEFINE_SCHED_CLASS(dl) = {
 
 	.wakeup_preempt		= wakeup_preempt_dl,
 
-	.pick_next_task		= pick_next_task_dl,
+	.pick_task		= pick_task_dl,
 	.put_prev_task		= put_prev_task_dl,
 	.set_next_task		= set_next_task_dl,
 
 #ifdef CONFIG_SMP
 	.balance		= balance_dl,
-	.pick_task		= pick_task_dl,
 	.select_task_rq		= select_task_rq_dl,
 	.migrate_task_rq	= migrate_task_rq_dl,
 	.set_cpus_allowed       = set_cpus_allowed_dl,

kernel/sched/ext.c

@@ -2719,7 +2719,8 @@ static void process_ddsp_deferred_locals(struct rq *rq)
 	}
 }
 
-static void put_prev_task_scx(struct rq *rq, struct task_struct *p)
+static void put_prev_task_scx(struct rq *rq, struct task_struct *p,
+			      struct task_struct *next)
 {
 	update_curr_scx(rq);
 
@@ -2774,14 +2775,21 @@ static struct task_struct *first_local_task(struct rq *rq)
 					struct task_struct, scx.dsq_list.node);
 }
 
-static struct task_struct *pick_next_task_scx(struct rq *rq)
+static struct task_struct *pick_next_task_scx(struct rq *rq,
+					      struct task_struct *prev)
 {
 	struct task_struct *p;
 
+	if (prev->sched_class == &ext_sched_class)
+		put_prev_task_scx(rq, prev, NULL);
+
 	p = first_local_task(rq);
 	if (!p)
 		return NULL;
 
+	if (prev->sched_class != &ext_sched_class)
+		prev->sched_class->put_prev_task(rq, prev, p);
+
 	set_next_task_scx(rq, p, true);
 
 	if (unlikely(!p->scx.slice)) {

kernel/sched/fair.c

@@ -5457,6 +5457,13 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
 
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
 
+static inline void finish_delayed_dequeue_entity(struct sched_entity *se)
+{
+	se->sched_delayed = 0;
+	if (sched_feat(DELAY_ZERO) && se->vlag > 0)
+		se->vlag = 0;
+}
+
 static bool
 dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
@@ -5532,11 +5539,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) != DEQUEUE_SAVE)
 		update_min_vruntime(cfs_rq);
 
-	if (flags & DEQUEUE_DELAYED) {
+	if (flags & DEQUEUE_DELAYED)
-		se->sched_delayed = 0;
+		finish_delayed_dequeue_entity(se);
-		if (sched_feat(DELAY_ZERO) && se->vlag > 0)
-			se->vlag = 0;
-	}
 
 	if (cfs_rq->nr_running == 0)
 		update_idle_cfs_rq_clock_pelt(cfs_rq);
@@ -8746,17 +8750,12 @@ static struct task_struct *pick_task_fair(struct rq *rq)
 		cfs_rq = group_cfs_rq(se);
 	} while (cfs_rq);
 
-	/*
-	 * This can be called from directly from CFS's ->pick_task() or indirectly
-	 * from DL's ->pick_task when fair server is enabled. In the indirect case,
-	 * DL will set ->dl_server just after this function is called, so its Ok to
-	 * clear. In the direct case, we are picking directly so we must clear it.
-	 */
-	task_of(se)->dl_server = NULL;
-
 	return task_of(se);
 }
 
+static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool first);
+static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first);
+
 struct task_struct *
 pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 {
@@ -8771,9 +8770,11 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 	se = &p->se;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-	if (!prev || prev->sched_class != &fair_sched_class)
+	if (prev->sched_class != &fair_sched_class)
 		goto simple;
 
+	__put_prev_set_next_dl_server(rq, prev, p);
+
 	/*
 	 * Because of the set_next_buddy() in dequeue_task_fair() it is rather
 	 * likely that a next task is from the same cgroup as the current.
@@ -8805,33 +8806,15 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 
 		put_prev_entity(cfs_rq, pse);
 		set_next_entity(cfs_rq, se);
+
+		__set_next_task_fair(rq, p, true);
 	}
 
-	goto done;
+	return p;
+
 simple:
 #endif
-	if (prev)
+	put_prev_set_next_task(rq, prev, p);
-		put_prev_task(rq, prev);
-
-	for_each_sched_entity(se)
-		set_next_entity(cfs_rq_of(se), se);
-
-done: __maybe_unused;
-#ifdef CONFIG_SMP
-	/*
-	 * Move the next running task to the front of
-	 * the list, so our cfs_tasks list becomes MRU
-	 * one.
-	 */
-	list_move(&p->se.group_node, &rq->cfs_tasks);
-#endif
-
-	if (hrtick_enabled_fair(rq))
-		hrtick_start_fair(rq, p);
-
-	update_misfit_status(p, rq);
-	sched_fair_update_stop_tick(rq, p);
-
 	return p;
 
 idle:
@@ -8860,9 +8843,9 @@ done: __maybe_unused;
 	return NULL;
 }
 
-static struct task_struct *__pick_next_task_fair(struct rq *rq)
+static struct task_struct *__pick_next_task_fair(struct rq *rq, struct task_struct *prev)
 {
-	return pick_next_task_fair(rq, NULL, NULL);
+	return pick_next_task_fair(rq, prev, NULL);
 }
 
 static bool fair_server_has_tasks(struct sched_dl_entity *dl_se)
@@ -8872,16 +8855,7 @@ static bool fair_server_has_tasks(struct sched_dl_entity *dl_se)
 
 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)
@@ -8890,15 +8864,13 @@ 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,
+	dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick_task);
-		       fair_server_pick_task);
-
 }
 
 /*
  * Account for a descheduled task:
  */
-static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
+static void put_prev_task_fair(struct rq *rq, struct task_struct *prev, struct task_struct *next)
 {
 	struct sched_entity *se = &prev->se;
 	struct cfs_rq *cfs_rq;
@@ -13098,11 +13070,16 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
 	 * and we cannot use DEQUEUE_DELAYED.
 	 */
 	if (p->se.sched_delayed) {
+		/* First, dequeue it from its new class' structures */
 		dequeue_task(rq, p, DEQUEUE_NOCLOCK | DEQUEUE_SLEEP);
-		p->se.sched_delayed = 0;
+		/*
+		 * Now, clean up the fair_sched_class side of things
+		 * related to sched_delayed being true and that wasn't done
+		 * due to the generic dequeue not using DEQUEUE_DELAYED.
+		 */
+		finish_delayed_dequeue_entity(&p->se);
 		p->se.rel_deadline = 0;
-		if (sched_feat(DELAY_ZERO) && p->se.vlag > 0)
+		__block_task(rq, p);
-			p->se.vlag = 0;
 	}
 }
 
@@ -13127,12 +13104,7 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p)
 	}
 }
 
-/* Account for a task changing its policy or group.
+static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
- *
- * This routine is mostly called to set cfs_rq->curr field when a task
- * migrates between groups/classes.
- */
-static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 {
 	struct sched_entity *se = &p->se;
 
@@ -13145,6 +13117,27 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 		list_move(&se->group_node, &rq->cfs_tasks);
 	}
 #endif
+	if (!first)
+		return;
+
+	SCHED_WARN_ON(se->sched_delayed);
+
+	if (hrtick_enabled_fair(rq))
+		hrtick_start_fair(rq, p);
+
+	update_misfit_status(p, rq);
+	sched_fair_update_stop_tick(rq, p);
+}
+
+/*
+ * Account for a task changing its policy or group.
+ *
+ * This routine is mostly called to set cfs_rq->curr field when a task
+ * migrates between groups/classes.
+ */
+static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
+{
+	struct sched_entity *se = &p->se;
 
 	for_each_sched_entity(se) {
 		struct cfs_rq *cfs_rq = cfs_rq_of(se);
@@ -13154,10 +13147,7 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 		account_cfs_rq_runtime(cfs_rq, 0);
 	}
 
-	if (!first)
+	__set_next_task_fair(rq, p, first);
-		return;
-
-	SCHED_WARN_ON(se->sched_delayed);
 }
 
 void init_cfs_rq(struct cfs_rq *cfs_rq)
@@ -13483,13 +13473,13 @@ DEFINE_SCHED_CLASS(fair) = {
 
 	.wakeup_preempt		= check_preempt_wakeup_fair,
 
+	.pick_task		= pick_task_fair,
 	.pick_next_task		= __pick_next_task_fair,
 	.put_prev_task		= put_prev_task_fair,
 	.set_next_task          = set_next_task_fair,
 
 #ifdef CONFIG_SMP
 	.balance		= balance_fair,
-	.pick_task		= pick_task_fair,
 	.select_task_rq		= select_task_rq_fair,
 	.migrate_task_rq	= migrate_task_rq_fair,
 

kernel/sched/idle.c

@@ -450,7 +450,7 @@ static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags)
 	resched_curr(rq);
 }
 
-static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
+static void put_prev_task_idle(struct rq *rq, struct task_struct *prev, struct task_struct *next)
 {
 	dl_server_update_idle_time(rq, prev);
 	scx_update_idle(rq, false);
@@ -464,21 +464,10 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir
 	next->se.exec_start = rq_clock_task(rq);
 }
 
-#ifdef CONFIG_SMP
+struct task_struct *pick_task_idle(struct rq *rq)
-static struct task_struct *pick_task_idle(struct rq *rq)
 {
 	return rq->idle;
 }
-#endif
-
-struct task_struct *pick_next_task_idle(struct rq *rq)
-{
-	struct task_struct *next = rq->idle;
-
-	set_next_task_idle(rq, next, true);
-
-	return next;
-}
 
 /*
  * It is not legal to sleep in the idle task - print a warning
@@ -533,13 +522,12 @@ DEFINE_SCHED_CLASS(idle) = {
 
 	.wakeup_preempt		= wakeup_preempt_idle,
 
-	.pick_next_task		= pick_next_task_idle,
+	.pick_task		= pick_task_idle,
 	.put_prev_task		= put_prev_task_idle,
 	.set_next_task          = set_next_task_idle,
 
 #ifdef CONFIG_SMP
 	.balance		= balance_idle,
-	.pick_task		= pick_task_idle,
 	.select_task_rq		= select_task_rq_idle,
 	.set_cpus_allowed	= set_cpus_allowed_common,
 #endif

kernel/sched/rt.c

@@ -1748,17 +1748,7 @@ static struct task_struct *pick_task_rt(struct rq *rq)
 	return p;
 }
 
-static struct task_struct *pick_next_task_rt(struct rq *rq)
+static void put_prev_task_rt(struct rq *rq, struct task_struct *p, struct task_struct *next)
-{
-	struct task_struct *p = pick_task_rt(rq);
-
-	if (p)
-		set_next_task_rt(rq, p, true);
-
-	return p;
-}
-
-static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
 {
 	struct sched_rt_entity *rt_se = &p->rt;
 	struct rt_rq *rt_rq = &rq->rt;
@@ -2645,13 +2635,12 @@ DEFINE_SCHED_CLASS(rt) = {
 
 	.wakeup_preempt		= wakeup_preempt_rt,
 
-	.pick_next_task		= pick_next_task_rt,
+	.pick_task		= pick_task_rt,
 	.put_prev_task		= put_prev_task_rt,
 	.set_next_task          = set_next_task_rt,
 
 #ifdef CONFIG_SMP
 	.balance		= balance_rt,
-	.pick_task		= pick_task_rt,
 	.select_task_rq		= select_task_rq_rt,
 	.set_cpus_allowed       = set_cpus_allowed_common,
 	.rq_online              = rq_online_rt,

kernel/sched/sched.h

@@ -389,7 +389,6 @@ extern void dl_server_start(struct sched_dl_entity *dl_se);
 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,
@@ -1133,6 +1132,7 @@ struct rq {
 	unsigned int		nr_uninterruptible;
 
 	struct task_struct __rcu	*curr;
+	struct sched_dl_entity	*dl_server;
 	struct task_struct	*idle;
 	struct task_struct	*stop;
 	unsigned long		next_balance;
@@ -1260,6 +1260,7 @@ struct rq {
 	/* per rq */
 	struct rq		*core;
 	struct task_struct	*core_pick;
+	struct sched_dl_entity	*core_dl_server;
 	unsigned int		core_enabled;
 	unsigned int		core_sched_seq;
 	struct rb_root		core_tree;
@@ -2368,9 +2369,19 @@ struct sched_class {
 	void (*wakeup_preempt)(struct rq *rq, struct task_struct *p, int flags);
 
 	int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
-	struct task_struct *(*pick_next_task)(struct rq *rq);
+	struct task_struct *(*pick_task)(struct rq *rq);
+	/*
+	 * Optional! When implemented pick_next_task() should be equivalent to:
+	 *
+	 *   next = pick_task();
+	 *   if (next) {
+	 *       put_prev_task(prev);
+	 *       set_next_task_first(next);
+	 *   }
+	 */
+	struct task_struct *(*pick_next_task)(struct rq *rq, struct task_struct *prev);
 
-	void (*put_prev_task)(struct rq *rq, struct task_struct *p);
+	void (*put_prev_task)(struct rq *rq, struct task_struct *p, struct task_struct *next);
 	void (*set_next_task)(struct rq *rq, struct task_struct *p, bool first);
 
 	void (*switch_class)(struct rq *rq, struct task_struct *next);
@@ -2378,8 +2389,6 @@ struct sched_class {
 #ifdef CONFIG_SMP
 	int  (*select_task_rq)(struct task_struct *p, int task_cpu, int flags);
 
-	struct task_struct * (*pick_task)(struct rq *rq);
-
 	void (*migrate_task_rq)(struct task_struct *p, int new_cpu);
 
 	void (*task_woken)(struct rq *this_rq, struct task_struct *task);
@@ -2426,7 +2435,7 @@ struct sched_class {
 static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
 {
 	WARN_ON_ONCE(rq->curr != prev);
-	prev->sched_class->put_prev_task(rq, prev);
+	prev->sched_class->put_prev_task(rq, prev, NULL);
 }
 
 static inline void set_next_task(struct rq *rq, struct task_struct *next)
@@ -2434,6 +2443,30 @@ static inline void set_next_task(struct rq *rq, struct task_struct *next)
 	next->sched_class->set_next_task(rq, next, false);
 }
 
+static inline void
+__put_prev_set_next_dl_server(struct rq *rq,
+			      struct task_struct *prev,
+			      struct task_struct *next)
+{
+	prev->dl_server = NULL;
+	next->dl_server = rq->dl_server;
+	rq->dl_server = NULL;
+}
+
+static inline void put_prev_set_next_task(struct rq *rq,
+					  struct task_struct *prev,
+					  struct task_struct *next)
+{
+	WARN_ON_ONCE(rq->curr != prev);
+
+	__put_prev_set_next_dl_server(rq, prev, next);
+
+	if (next == prev)
+		return;
+
+	prev->sched_class->put_prev_task(rq, prev, next);
+	next->sched_class->set_next_task(rq, next, true);
+}
 
 /*
  * Helper to define a sched_class instance; each one is placed in a separate
@@ -2524,7 +2557,7 @@ static inline bool sched_fair_runnable(struct rq *rq)
 }
 
 extern struct task_struct *pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
-extern struct task_struct *pick_next_task_idle(struct rq *rq);
+extern struct task_struct *pick_task_idle(struct rq *rq);
 
 #define SCA_CHECK		0x01
 #define SCA_MIGRATE_DISABLE	0x02

kernel/sched/stop_task.c

@@ -41,16 +41,6 @@ static struct task_struct *pick_task_stop(struct rq *rq)
 	return rq->stop;
 }
 
-static struct task_struct *pick_next_task_stop(struct rq *rq)
-{
-	struct task_struct *p = pick_task_stop(rq);
-
-	if (p)
-		set_next_task_stop(rq, p, true);
-
-	return p;
-}
-
 static void
 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 {
@@ -69,7 +59,7 @@ static void yield_task_stop(struct rq *rq)
 	BUG(); /* the stop task should never yield, its pointless. */
 }
 
-static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
+static void put_prev_task_stop(struct rq *rq, struct task_struct *prev, struct task_struct *next)
 {
 	update_curr_common(rq);
 }
@@ -112,13 +102,12 @@ DEFINE_SCHED_CLASS(stop) = {
 
 	.wakeup_preempt		= wakeup_preempt_stop,
 
-	.pick_next_task		= pick_next_task_stop,
+	.pick_task		= pick_task_stop,
 	.put_prev_task		= put_prev_task_stop,
 	.set_next_task          = set_next_task_stop,
 
 #ifdef CONFIG_SMP
 	.balance		= balance_stop,
-	.pick_task		= pick_task_stop,
 	.select_task_rq		= select_task_rq_stop,
 	.set_cpus_allowed	= set_cpus_allowed_common,
 #endif