linux-kernel - [PATCH v3 5/7] sched/deadline: Optimize find_later

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Date:	Wed,  5 Nov 2014 23:48:24 +0800
From:	"pang.xunlei" <pang.xunlei@...aro.org>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Juri Lelli <juri.lelli@...il.com>,
	"pang.xunlei" <pang.xunlei@...aro.org>
Subject: [PATCH v3 5/7] sched/deadline: Optimize find_later_rq() to select a cache hot cpu

Add the case for iteration of sched_domains without SD_WAKE_AFFINE
flags to select a cpu, this flag may be unset through proc by users.

Signed-off-by: pang.xunlei <pang.xunlei@...aro.org>
---
 kernel/sched/deadline.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 42edfcd..ddb6185 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1165,6 +1165,7 @@ static int find_later_rq(struct task_struct *task)
 	struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
 	int this_cpu = smp_processor_id();
 	int cpu = task_cpu(task);
+	int cachehot_cpu = nr_cpu_ids;
 
 	/* Make sure the mask is initialized first */
 	if (unlikely(!later_mask))
@@ -1209,7 +1210,7 @@ static int find_later_rq(struct task_struct *task)
 
 	rcu_read_lock();
 	for_each_domain(cpu, sd) {
-		int best_cpu;
+		int wakeaffine_cpu;
 		if (sd->flags & SD_WAKE_AFFINE) {
 
 			/*
@@ -1222,16 +1223,24 @@ static int find_later_rq(struct task_struct *task)
 				return this_cpu;
 			}
 
-			best_cpu = cpumask_first_and(later_mask,
-								sched_domain_span(sd));
-			if (best_cpu < nr_cpu_ids) {
+			wakeaffine_cpu = cpumask_first_and(later_mask,
+							 sched_domain_span(sd));
+			if (wakeaffine_cpu < nr_cpu_ids) {
 				rcu_read_unlock();
-				return best_cpu;
+				return wakeaffine_cpu;
 			}
+		} else {
+			if (cachehot_cpu >= nr_cpu_ids)
+				cachehot_cpu = cpumask_first_and(later_mask,
+							   sched_domain_span(sd));
 		}
 	}
 	rcu_read_unlock();
 
+	/* Most likely cache-hot */
+	if (cachehot_cpu < nr_cpu_ids)
+		return cachehot_cpu;
+
 	/*
 	 * At this point, all our guesses failed, we just return
 	 * 'something', and let the caller sort the things out.
-- 
2.1.0

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