linux-kernel - [PATCH v3 3/7] sched: rotate the cpu search window for better spread

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Date:   Sat,  8 Jun 2019 18:49:50 -0700
From:   subhra mazumdar <subhra.mazumdar@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, steven.sistare@...cle.com,
        dhaval.giani@...cle.com, daniel.lezcano@...aro.org,
        vincent.guittot@...aro.org, viresh.kumar@...aro.org,
        tim.c.chen@...ux.intel.com, mgorman@...hsingularity.net
Subject: [PATCH v3 3/7] sched: rotate the cpu search window for better spread

Rotate the cpu search window for better spread of threads. This will ensure
an idle cpu will quickly be found if one exists.

Signed-off-by: subhra mazumdar <subhra.mazumdar@...cle.com>
---
 kernel/sched/fair.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b58f08f..c1ca88e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6188,7 +6188,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 	u64 avg_cost, avg_idle;
 	u64 time, cost;
 	s64 delta;
-	int cpu, limit, floor, nr = INT_MAX;
+	int cpu, limit, floor, target_tmp, nr = INT_MAX;
 
 	this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
 	if (!this_sd)
@@ -6219,9 +6219,15 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 		}
 	}
 
+	if (per_cpu(next_cpu, target) != -1)
+		target_tmp = per_cpu(next_cpu, target);
+	else
+		target_tmp = target;
+
 	time = local_clock();
 
-	for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
+	for_each_cpu_wrap(cpu, sched_domain_span(sd), target_tmp) {
+		per_cpu(next_cpu, target) = cpu;
 		if (!--nr)
 			return -1;
 		if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
-- 
2.9.3