linux-kernel - BFS 420: cleanup try

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Date:	Thu, 17 May 2012 20:47:45 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Hillf Danton <dhillf@...il.com>
Subject: BFS 420: cleanup try_preempt

First the cpumask on stack is removed.

Then before scanning online CPUs, highest_prio and latest_deadline are inited
with values of the given task, for shortening the scan as much as we could.

And if we get highest_prio_rq, its current task is rescheduled without bothering
calling can_preempt, as we already do the checks when finding the
target runqueue.


--- a/kernel/sched/bfs.c	Mon May 14 20:50:38 2012
+++ b/kernel/sched/bfs.c	Thu May 17 20:35:46 2012
@@ -1423,7 +1423,6 @@ static void try_preempt(struct task_stru
 	struct rq *highest_prio_rq = NULL;
 	int cpu, highest_prio;
 	u64 latest_deadline;
-	cpumask_t tmp;

 	/*
 	 * We clear the sticky flag here because for a task to have called
@@ -1441,14 +1440,10 @@ static void try_preempt(struct task_stru
 	if (p->policy == SCHED_IDLEPRIO)
 		return;

-	if (likely(online_cpus(p)))
-		cpus_and(tmp, cpu_online_map, p->cpus_allowed);
-	else
-		return;
-
-	highest_prio = latest_deadline = 0;
+	highest_prio = p->prio;
+	latest_deadline = p->deadline;

-	for_each_cpu_mask(cpu, tmp) {
+	for_each_cpu_and(cpu, cpu_online_map, p->cpus_allowed) {
 		struct rq *rq;
 		int rq_prio;

@@ -1465,10 +1460,8 @@ static void try_preempt(struct task_stru
 		}
 	}

-	if (likely(highest_prio_rq)) {
-		if (can_preempt(p, highest_prio, highest_prio_rq->rq_deadline))
-			resched_task(highest_prio_rq->curr);
-	}
+	if (highest_prio_rq)
+		resched_task(highest_prio_rq->curr);
 }
 #else /* CONFIG_SMP */
 static inline bool needs_other_cpu(struct task_struct *p, int cpu)
--
--
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