linux-kernel - [PATCH] sched/deadline: Add update_rq_clock() in yield_task

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Date:	Fri, 19 Dec 2014 00:31:03 +0800
From:	Xunlei Pang <pang.xunlei@...aro.org>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...il.com>,
	Xunlei Pang <pang.xunlei@...aro.org>
Subject: [PATCH] sched/deadline: Add update_rq_clock() in yield_task_dl()

yield_task_dl() calls update_curr_dl() which calls start_dl_timer()
to throttle current task. But yield_task_dl() doesn't update the rq
clock which will cause start_dl_timer() to set the wrong dl_timer
which may be much later than current deadline time.

For instance, in systems with 100HZ tick, if there're few dl-tasks,
then rq clock will mainly depend on the tick to update its value.
If we choose the CONFIG_NO_HZ_FULL_ALL feature, things may get even
worse.

Moreover, there're some statistics in update_curr_dl() also relying
on rq clock, like rq_clock_task().

Thus, in yield_task_dl(), we should add update_rq_clock() before
update_curr_dl().

Signed-off-by: Xunlei Pang <pang.xunlei@...aro.org>
---
 kernel/sched/deadline.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e5db8c6..5648e62 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -915,7 +915,11 @@ static void yield_task_dl(struct rq *rq)
 		rq->curr->dl.dl_yielded = 1;
 		p->dl.runtime = 0;
 	}
+
+	update_rq_clock(rq);
 	update_curr_dl(rq);
+	/* Will go to schedule(), to avoid another clock update. */
+	rq->skip_clock_update = 1;
 }

 #ifdef CONFIG_SMP
-- 
1.9.1

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