linux-kernel - [PATCH v2 1/2] sched/deadline: Remove unnecessary condition in push_dl

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Date:   Thu, 16 Feb 2017 11:05:53 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     <peterz@...radead.org>, <mingo@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <juri.lelli@...il.com>,
        <rostedt@...dmis.org>, <kernel-team@....com>
Subject: [PATCH v2 1/2] sched/deadline: Remove unnecessary condition in push_dl_task()

Once pick_next_pushable_dl_task(rq) returns a task, it guarantees that
the task's cpu is rq->cpu, so task_cpu(next_task) is always rq->cpu if
task == next_task. Remove the redundant condition and make code simpler.

pick_next_pushable_dl_task(rq) has BUG_ON(rq->cpu != task_cpu(task))
when it returns a task other than NULL, which means that task_cpu(task)
must be rq->cpu. So if task == next_task, then task_cpu(next_task) must
be rq->cpu as well.

By this patch, unnecessary one branch and two LOAD operations in 'if'
statement can be avoided.

Signed-off-by: Byungchul Park <byungchul.park@....com>
---
 kernel/sched/deadline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 27737f3..ad8d577 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1483,7 +1483,7 @@ static int push_dl_task(struct rq *rq)
 		 * then possible that next_task has migrated.
 		 */
 		task = pick_next_pushable_dl_task(rq);
-		if (task_cpu(next_task) == rq->cpu && task == next_task) {
+		if (task == next_task) {
 			/*
 			 * The task is still there. We don't try
 			 * again, some other cpu will pull it when ready.
-- 
1.9.1