linux-kernel - [tip:sched/urgent] sched/rt: Make update_curr

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Date:   Tue, 13 Feb 2018 03:28:45 -0800
From:   tip-bot for Wen Yang <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     jiang.biao2@....com.cn, hpa@...or.com, wen.yang99@....com.cn,
        tglx@...utronix.de, torvalds@...ux-foundation.org,
        peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip:sched/urgent] sched/rt: Make update_curr_rt() more accurate

Commit-ID:  a7711602c7b79950ea437178f601b52ab08ef659
Gitweb:     https://git.kernel.org/tip/a7711602c7b79950ea437178f601b52ab08ef659
Author:     Wen Yang <wen.yang99@....com.cn>
AuthorDate: Tue, 6 Feb 2018 09:53:28 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 13 Feb 2018 11:44:41 +0100

sched/rt: Make update_curr_rt() more accurate

rq->clock_task may be updated between the two calls of
rq_clock_task() in update_curr_rt(). Calling rq_clock_task() only
once makes it more accurate and efficient, taking update_curr() as
reference.

Signed-off-by: Wen Yang <wen.yang99@....com.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Jiang Biao <jiang.biao2@....com.cn>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: zhong.weidong@....com.cn
Link: http://lkml.kernel.org/r/1517882008-44552-1-git-send-email-wen.yang99@zte.com.cn
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/rt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 663b235..aad49451 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -950,12 +950,13 @@ static void update_curr_rt(struct rq *rq)
 {
 	struct task_struct *curr = rq->curr;
 	struct sched_rt_entity *rt_se = &curr->rt;
-	u64 now = rq_clock_task(rq);
 	u64 delta_exec;
+	u64 now;
 
 	if (curr->sched_class != &rt_sched_class)
 		return;
 
+	now = rq_clock_task(rq);
 	delta_exec = now - curr->se.exec_start;
 	if (unlikely((s64)delta_exec <= 0))
 		return;