sched/rt: Make update_curr_rt() more accurate

Web:        https://git.kernel.org/torvalds/c/a7711602c7b79950ea437178f601b52ab08ef659
Commit:     a7711602c7b79950ea437178f601b52ab08ef659
Parent:     6fe0ce1eb04f99a1eb1eb6e7f775666966cf6c80
Refname:    refs/heads/master
Author:     Wen Yang <[email protected]>
AuthorDate: Tue Feb 6 09:53:28 2018 +0800
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue Feb 13 11:44:41 2018 +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 <[email protected]>
    Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
    Reviewed-by: Jiang Biao <[email protected]>
    Cc: Linus Torvalds <[email protected]>
    Cc: Peter Zijlstra <[email protected]>
    Cc: Thomas Gleixner <[email protected]>
    Cc: [email protected]
    Link: http://lkml.kernel.org/r/[email protected]
    Signed-off-by: Ingo Molnar <[email protected]>
---
 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 663b2355a3aa..aad49451584e 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;
--
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