linux-kernel - [PATCH 2/9] sched: Fixup set_next

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Message-Id: <20240813224015.724111109@infradead.org>
Date: Wed, 14 Aug 2024 00:25:50 +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 2/9] sched: Fixup set_next_task() implementations

The rule is that:

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

Turns out, there's still a few things in pick_next_task() that are
missing from that combination.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/deadline.c |    6 ++--
 kernel/sched/fair.c     |   62 ++++++++++++++++++++++++------------------------
 2 files changed, 34 insertions(+), 34 deletions(-)

--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2392,6 +2392,9 @@ static void set_next_task_dl(struct rq *
 		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)
@@ -2458,9 +2461,6 @@ static struct task_struct *pick_next_tas
 	if (!p->dl_server)
 		set_next_task_dl(rq, p, true);
 
-	if (hrtick_enabled(rq))
-		start_hrtick_dl(rq, &p->dl);
-
 	return p;
 }
 
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8758,6 +8758,9 @@ static struct task_struct *pick_task_fai
 	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)
 {
@@ -8806,33 +8809,17 @@ pick_next_task_fair(struct rq *rq, struc
 
 		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_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);
-
+	set_next_task_fair(rq, p, true);
 	return p;
 
 idle:
@@ -13142,12 +13129,7 @@ static void switched_to_fair(struct rq *
 	}
 }
 
-/* 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)
+static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 {
 	struct sched_entity *se = &p->se;
 
@@ -13160,6 +13142,27 @@ static void set_next_task_fair(struct rq
 		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);
@@ -13169,10 +13172,7 @@ static void set_next_task_fair(struct rq
 		account_cfs_rq_runtime(cfs_rq, 0);
 	}
 
-	if (!first)
-		return;
-
-	SCHED_WARN_ON(se->sched_delayed);
+	__set_next_task_fair(rq, p, first);
 }
 
 void init_cfs_rq(struct cfs_rq *cfs_rq)