From: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Date: Fri, 24 Aug 2007 18:39:10 +0000 (+0200)
Subject: sched: optimize task_tick_rt() a bit
X-Git-Tag: v5.15~46348^2~4
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=98fbc798533339be802c6dcd48c2293c712e87db;p=mirror_ubuntu-kernels.git

sched: optimize task_tick_rt() a bit

Mitchell Erblich suggested a quality-of-implementation change to
not requeue SCHED_RR tasks if there's only a single task on the
runqueue, by checking for rq->nr_running == 1.

provide a more efficient implementation of that, to check that
particular RT priority-queue only.

[ From: mingo@elte.hu ]

Also first requeue the task then set need_resched - results in slightly
better machine-instruction ordering. Also clean up the code a bit.

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index dcdcad632fd9..4b87476a02d0 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -207,10 +207,15 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p)
 		return;
 
 	p->time_slice = static_prio_timeslice(p->static_prio);
-	set_tsk_need_resched(p);
 
-	/* put it at the end of the queue: */
-	requeue_task_rt(rq, p);
+	/*
+	 * Requeue to the end of queue if we are not the only element
+	 * on the queue:
+	 */
+	if (p->run_list.prev != p->run_list.next) {
+		requeue_task_rt(rq, p);
+		set_tsk_need_resched(p);
+	}
 }
 
 static struct sched_class rt_sched_class __read_mostly = {