linux-kernel - [PATCH v3 1/5] sched/deadline: fix try to pull pinned dl tasks in pull algorithm

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Message-ID: <BLU437-SMTP970E064CF114DF6BCE358180B70@phx.gbl>
Date:	Sun, 31 May 2015 08:26:57 +0800
From:	Wanpeng Li <wanpeng.li@...mail.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@...mail.com>
Subject: [PATCH v3 1/5] sched/deadline: fix try to pull pinned dl tasks in pull algorithm

Function pick_next_earliest_dl_task is used to pick earliest and pushable
dl task from overloaded cpus in pull algorithm, however, it traverses
runqueue rbtree instead of pushable task rbtree which is also ordered by
tasks' deadlines. This will result in getting no candidates from overloaded
cpus if all the dl tasks on the overloaded cpus are pinned. This patch fix
it by traversing pushable task rbtree which is also ordered by tasks'
deadlines.

Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 kernel/sched/deadline.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 890ce95..f09f3ad 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1230,6 +1230,33 @@ next_node:
 	return NULL;
 }
 
+/*
+ * Return the earliest pushable rq's task, which is suitable to be executed
+ * on the cpu, NULL otherwse
+ */
+static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq,
+									int cpu)
+{
+	struct rb_node *next_node = rq->dl.pushable_dl_tasks_leftmost;
+	struct task_struct *p = NULL;
+
+	if (!has_pushable_dl_tasks(rq))
+		return NULL;
+
+next_node:
+	if (next_node) {
+		p = rb_entry(next_node, struct task_struct, pushable_dl_tasks);
+
+		if (pick_dl_task(rq, p, cpu))
+			return p;
+
+		next_node = rb_next(next_node);
+		goto next_node;
+	}
+
+	return NULL;
+}
+
 static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
 
 static int find_later_rq(struct task_struct *task)
@@ -1514,7 +1541,7 @@ static int pull_dl_task(struct rq *this_rq)
 		if (src_rq->dl.dl_nr_running <= 1)
 			goto skip;
 
-		p = pick_next_earliest_dl_task(src_rq, this_cpu);
+		p = pick_earliest_pushable_dl_task(src_rq, this_cpu);
 
 		/*
 		 * We found a task to be pulled if:
-- 
1.9.1

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