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From:   subhra mazumdar <subhra.mazumdar@oracle.com>
To:     linux-kernel@vger.kernel.org
Cc:     peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de,
        steven.sistare@oracle.com, dhaval.giani@oracle.com,
        daniel.lezcano@linaro.org, vincent.guittot@linaro.org,
        viresh.kumar@linaro.org, tim.c.chen@linux.intel.com,
        mgorman@techsingularity.net, parth@linux.ibm.com,
        patrick.bellasi@arm.com
Subject: [RFC PATCH 9/9] sched: rotate the cpu search window for better spread
Date:   Fri, 30 Aug 2019 10:49:44 -0700
Message-Id: <20190830174944.21741-10-subhra.mazumdar@oracle.com>
In-Reply-To: <20190830174944.21741-1-subhra.mazumdar@oracle.com>
References: <20190830174944.21741-1-subhra.mazumdar@oracle.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@oracle.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 94dd4a32..7419b47 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, floor, nr = INT_MAX;
+	int cpu, floor, target_tmp, nr = INT_MAX;
 
 	this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
 	if (!this_sd)
@@ -6213,9 +6213,15 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 			nr = floor;
 	}
 
+	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