[PATCH] sched/rt: Make update_curr_rt() more accurate

[Wen Yang]

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.yan...@zte.com.cn>
Reviewed-by: Jiang Biao <jiang.bi...@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