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From:   Wen Yang <wen.yang99@zte.com.cn>
To:     mingo@redhat.com, peterz@infradead.org
Cc:     linux-kernel@vger.kernel.org, jiang.biao2@zte.com.cn,
        zhong.weidong@zte.com.cn, wen.yang99@zte.com.cn
Subject: [PATCH] sched/rt: Make update_curr_rt() more accurate
Date:   Mon, 5 Feb 2018 11:18:41 +0800
Message-Id: <1517800721-42092-1-git-send-email-wen.yang99@zte.com.cn>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@zte.com.cn>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
---
 kernel/sched/rt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4056c19..d6d2a65 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;
 
 	if (curr->sched_class != &rt_sched_class)
 		return;
 
-	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
+	delta_exec = now - curr->se.exec_start;
 	if (unlikely((s64)delta_exec <= 0))
 		return;
 
@@ -968,7 +969,7 @@ static void update_curr_rt(struct rq *rq)
 	curr->se.sum_exec_runtime += delta_exec;
 	account_group_exec_runtime(curr, delta_exec);
 
-	curr->se.exec_start = rq_clock_task(rq);
+	curr->se.exec_start = now;
 	cgroup_account_cputime(curr, delta_exec);
 
 	sched_rt_avg_update(rq, delta_exec);
-- 
1.9.1