sched/deadline: Make update_curr_dl() more accurate

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

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: zhong.weidong@zte.com.cn
Link: http://lkml.kernel.org/r/1517882148-44599-1-git-send-email-wen.yang99@zte.com.cn
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 9bb0e0c..9df0978 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1153,6 +1153,7 @@ static void update_curr_dl(struct rq *rq)
        struct sched_dl_entity *dl_se = &curr->dl;
        u64 delta_exec, scaled_delta_exec;
        int cpu = cpu_of(rq);
+       u64 now;
 
        if (!dl_task(curr) || !on_dl_rq(dl_se))
                return;
@@ -1165,7 +1166,8 @@ static void update_curr_dl(struct rq *rq)
         * natural solution, but the full ramifications of this
         * approach need further study.
         */
-       delta_exec = rq_clock_task(rq) - curr->se.exec_start;
+       now = rq_clock_task(rq);
+       delta_exec = now - curr->se.exec_start;
        if (unlikely((s64)delta_exec <= 0)) {
                if (unlikely(dl_se->dl_yielded))
                        goto throttle;
@@ -1178,7 +1180,7 @@ static void update_curr_dl(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);