linux-kernel - [PATCH] sched/deadline: reduce rq lock contention by eliminating locking of non-feasible target

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Date:	Mon, 23 Mar 2015 16:56:34 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: [PATCH] sched/deadline: reduce rq lock contention by eliminating locking of non-feasible target

This patch adds checks that prevents futile attempts to move dl tasks to 
a CPU with active tasks of equal or earlier deadline. The same behavior as 
commit 80e3d87b2c55 ("sched/rt: Reduce rq lock contention by eliminating 
locking of non-feasible target") for rt class.

Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
---
 kernel/sched/deadline.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 19d716e..9577db0 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -955,7 +955,8 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
 	    (p->nr_cpus_allowed > 1)) {
 		int target = find_later_rq(p);
 
-		if (target != -1)
+		if (target != -1 &&
+			p->dl.deadline < cpu_rq(target)->dl.earliest_dl.curr)
 			cpu = target;
 	}
 	rcu_read_unlock();
-- 
1.9.1

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