linux-kernel - [PATCH v8 9/9] sched/fair: remove check_preempt_from

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Date:   Thu, 10 Nov 2022 18:50:09 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com
Cc:     qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, David.Laight@...lab.com,
        pjt@...gle.com, pavel@....cz, tj@...nel.org, qperret@...gle.com,
        tim.c.chen@...ux.intel.com, joshdon@...gle.com, timj@....org,
        kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v8 9/9] sched/fair: remove check_preempt_from_others

With the dedicated latency list, we don't have to take care of this special
case anymore as pick_next_entity checks for a runnable latency sensitive
task.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 34 ++--------------------------------
 1 file changed, 2 insertions(+), 32 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fb4973a87f25..c2c75d531612 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5801,35 +5801,6 @@ static int sched_idle_cpu(int cpu)
 }
 #endif
 
-static void set_next_buddy(struct sched_entity *se);
-
-static void check_preempt_from_others(struct cfs_rq *cfs, struct sched_entity *se)
-{
-	struct sched_entity *next;
-
-	if (se->latency_offset >= 0)
-		return;
-
-	if (cfs->nr_running <= 1)
-		return;
-	/*
-	 * When waking from another class, we don't need to check to preempt at
-	 * wakeup and don't set next buddy as a candidate for being picked in
-	 * priority.
-	 * In case of simultaneous wakeup when current is another class, the
-	 * latency sensitive tasks lost opportunity to preempt non sensitive
-	 * tasks which woke up simultaneously.
-	 */
-
-	if (cfs->next)
-		next = cfs->next;
-	else
-		next = __pick_first_entity(cfs);
-
-	if (next && wakeup_preempt_entity(next, se) == 1)
-		set_next_buddy(se);
-}
-
 /*
  * The enqueue_task method is called before nr_running is
  * increased. Here we update the fair scheduling stats and
@@ -5916,15 +5887,14 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	if (!task_new)
 		update_overutilized_status(rq);
 
-	if (rq->curr->sched_class != &fair_sched_class)
-		check_preempt_from_others(cfs_rq_of(&p->se), &p->se);
-
 enqueue_throttle:
 	assert_list_leaf_cfs_rq(rq);
 
 	hrtick_update(rq);
 }
 
+static void set_next_buddy(struct sched_entity *se);
+
 /*
  * The dequeue_task method is called before nr_running is
  * decreased. We remove the task from the rbtree and
-- 
2.17.1