linux-kernel - [tip:sched/core] sched/deadline: Fix hrtick for a non-leftmost task

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Message-ID: <tip-a7bebf488791aa1036f3e6629daf01d01f705dcb@git.kernel.org>
Date:	Wed, 4 Feb 2015 06:34:52 -0800
From:	tip-bot for Wanpeng Li <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	peterz@...radead.org, wanpeng.li@...ux.intel.com, mingo@...nel.org,
	hpa@...or.com, torvalds@...ux-foundation.org, tglx@...utronix.de,
	ktkhai@...allels.com, linux-kernel@...r.kernel.org,
	juri.lelli@....com
Subject: [tip:sched/core] sched/deadline:
  Fix hrtick for a non-leftmost task

Commit-ID:  a7bebf488791aa1036f3e6629daf01d01f705dcb
Gitweb:     http://git.kernel.org/tip/a7bebf488791aa1036f3e6629daf01d01f705dcb
Author:     Wanpeng Li <wanpeng.li@...ux.intel.com>
AuthorDate: Wed, 26 Nov 2014 08:44:01 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 4 Feb 2015 07:52:25 +0100

sched/deadline: Fix hrtick for a non-leftmost task

After update_curr_dl() the current task might not be the leftmost task
anymore. In that case do not start a new hrtick for it.

In this case NEED_RESCHED will be set and the next schedule will start
the hrtick for the new task if and when appropriate.

Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
Acked-by: Juri Lelli <juri.lelli@....com>
[ Rewrote the changelog and comment. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Kirill Tkhai <ktkhai@...allels.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/1416962647-76792-2-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/deadline.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e0e9c29..7b684f9 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1073,7 +1073,13 @@ static void task_tick_dl(struct rq *rq, struct task_struct *p, int queued)
 {
 	update_curr_dl(rq);
 
-	if (hrtick_enabled(rq) && queued && p->dl.runtime > 0)
+	/*
+	 * Even when we have runtime, update_curr_dl() might have resulted in us
+	 * not being the leftmost task anymore. In that case NEED_RESCHED will
+	 * be set and schedule() will start a new hrtick for the next task.
+	 */
+	if (hrtick_enabled(rq) && queued && p->dl.runtime > 0 &&
+	    is_leftmost(p, &rq->dl))
 		start_hrtick_dl(rq, p);
 }
 
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