linux-kernel - [tip:sched/core] sched/rt: Remove unnecessary condition in push_rt

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Message-ID: <tip-de16b91effdbf5aeff8346b99bcd0991a5362db9@git.kernel.org>
Date:   Tue, 23 May 2017 01:44:50 -0700
From:   tip-bot for Byungchul Park <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, linux-kernel@...r.kernel.org, peterz@...radead.org,
        byungchul.park@....com, mingo@...nel.org, bristot@...hat.com,
        torvalds@...ux-foundation.org, kernel-team@....com,
        tglx@...utronix.de, rostedt@...dmis.org, juri.lelli@....com
Subject: [tip:sched/core] sched/rt: Remove unnecessary condition in
 push_rt_task()

Commit-ID:  de16b91effdbf5aeff8346b99bcd0991a5362db9
Gitweb:     http://git.kernel.org/tip/de16b91effdbf5aeff8346b99bcd0991a5362db9
Author:     Byungchul Park <byungchul.park@....com>
AuthorDate: Fri, 12 May 2017 10:05:43 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 23 May 2017 10:01:33 +0200

sched/rt: Remove unnecessary condition in push_rt_task()

pick_next_pushable_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. Remove the redundant condition and make the code simpler.

This way one unnecessary branch and two LOAD operations can be avoided.

Signed-off-by: Byungchul Park <byungchul.park@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Reviewed-by: Juri Lelli <juri.lelli@....com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: <kernel-team@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1494551143-22219-1-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/rt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 979b734..c18b500 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1819,7 +1819,7 @@ retry:
 		 * pushing.
 		 */
 		task = pick_next_pushable_task(rq);
-		if (task_cpu(next_task) == rq->cpu && task == next_task) {
+		if (task == next_task) {
 			/*
 			 * The task hasn't migrated, and is still the next
 			 * eligible task, but we failed to find a run-queue