linux-kernel - [PATCH 3/7] sched: Make pick_next_task

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Date:   Fri, 08 Nov 2019 14:15:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, juri.lelli@...hat.com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de
Cc:     linux-kernel@...r.kernel.org, qperret@...gle.com,
        valentin.schneider@....com, qais.yousef@....com,
        ktkhai@...tuozzo.com, peterz@...radead.org
Subject: [PATCH 3/7] sched: Make pick_next_task_idle() more consistent

Only pick_next_task_fair() needs the @prev and @rf argument; these are
required to implement the cpu-cgroup optimization. None of the other
pick_next_task() methods need this. Make pick_next_task_idle() more
consistent.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/core.c |    6 ++++--
 kernel/sched/idle.c |    3 +--
 2 files changed, 5 insertions(+), 4 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3922,8 +3922,10 @@ pick_next_task(struct rq *rq, struct tas
 			goto restart;
 
 		/* Assumes fair_sched_class->next == idle_sched_class */
-		if (unlikely(!p))
-			p = idle_sched_class.pick_next_task(rq, prev, rf);
+		if (unlikely(!p)) {
+			put_prev_task(rq, prev);
+			p = idle_sched_class.pick_next_task(rq, NULL, NULL);
+		}
 
 		return p;
 	}
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -390,8 +390,7 @@ pick_next_task_idle(struct rq *rq, struc
 {
 	struct task_struct *next = rq->idle;
 
-	if (prev)
-		put_prev_task(rq, prev);
+	WARN_ON_ONCE(prev || rf);
 
 	set_next_task_idle(rq, next);