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[PATCH v4 5/5] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()

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It would be better to avoid pushing tasks to other cpu within
a SD_PREFER_SIBLING domain, instead, get more chances to check other
siblings.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/rt.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 979b734..6332b2ad 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1624,6 +1624,7 @@ static int find_lowest_rq(struct task_struct *task)
 	struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
 	int this_cpu = smp_processor_id();
 	int cpu      = task_cpu(task);
+	int fallback_cpu = -1;
 
 	/* Make sure the mask is initialized first */
 	if (unlikely(!lowest_mask))
@@ -1671,6 +1672,15 @@ static int find_lowest_rq(struct task_struct *task)
 			best_cpu = cpumask_first_and(lowest_mask,
 						     sched_domain_span(sd));
 			if (best_cpu < nr_cpu_ids) {
+				/*
+				 * If current domain is SD_PREFER_SIBLING
+				 * flaged, we have to get more chances to
+				 * check other siblings.
+				 */
+				if (sd->flags & SD_PREFER_SIBLING) {
+					fallback_cpu = best_cpu;
+					continue;
+				}
 				rcu_read_unlock();
 				return best_cpu;
 			}
@@ -1679,6 +1689,13 @@ static int find_lowest_rq(struct task_struct *task)
 	rcu_read_unlock();
 
 	/*
+	 * If fallback_cpu is valid, all our quesses failed *except* for
+	 * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
+	 */
+	if (fallback_cpu != -1)
+		return fallback_cpu;
+
+	/*
 	 * And finally, if there were no matches within the domains
 	 * just give the caller *something* to work with from the compatible
 	 * locations.
-- 
1.9.1

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[PATCH v4 0/5] Make find_later_rq() choose a closer cpu in topology Byungchul Park <byungchul.park@lge.com> - 2017-05-12 07:50 +0200
  [PATCH v4 3/5] sched/deadline: Change return value of cpudl_find() Byungchul Park <byungchul.park@lge.com> - 2017-05-12 07:50 +0200
  [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically Byungchul Park <byungchul.park@lge.com> - 2017-05-12 07:50 +0200
    Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements  atomically Steven Rostedt <rostedt@goodmis.org> - 2017-05-12 16:30 +0200
      Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically Juri Lelli <juri.lelli@arm.com> - 2017-05-15 10:40 +0200
        Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically Byungchul Park <byungchul.park@lge.com> - 2017-05-16 09:10 +0200
      Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically Byungchul Park <byungchul.park@lge.com> - 2017-05-16 09:00 +0200
        Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically Juri Lelli <juri.lelli@arm.com> - 2017-05-16 12:40 +0200
          Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements  atomically Steven Rostedt <rostedt@goodmis.org> - 2017-05-16 15:20 +0200
            Re: [PATCH v4 1/5] sched/deadline: Refer to cpudl.elements atomically Byungchul Park <byungchul.park@lge.com> - 2017-05-23 03:20 +0200
  [PATCH v4 4/5] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-05-12 08:00 +0200
  [PATCH v4 5/5] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park <byungchul.park@lge.com> - 2017-05-12 08:00 +0200

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