linux-kernel - [RFC PATCH 4/9] sched: SIS_CORE to disable idle core search

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Date:   Fri, 30 Aug 2019 10:49:39 -0700
From:   subhra mazumdar <subhra.mazumdar@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, tglx@...utronix.de,
        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, parth@...ux.ibm.com,
        patrick.bellasi@....com
Subject: [RFC PATCH 4/9] sched: SIS_CORE to disable idle core search

Use SIS_CORE to disable idle core search. For some workloads
select_idle_core becomes a scalability bottleneck, removing it improves
throughput. Also there are workloads where disabling it can hurt latency,
so need to have an option.

Signed-off-by: subhra mazumdar <subhra.mazumdar@...cle.com>
---
 kernel/sched/fair.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c31082d..23ec9c6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6268,9 +6268,11 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	if (!sd)
 		return target;
 
-	i = select_idle_core(p, sd, target);
-	if ((unsigned)i < nr_cpumask_bits)
-		return i;
+	if (sched_feat(SIS_CORE)) {
+		i = select_idle_core(p, sd, target);
+		if ((unsigned)i < nr_cpumask_bits)
+			return i;
+	}
 
 	i = select_idle_cpu(p, sd, target);
 	if ((unsigned)i < nr_cpumask_bits)
-- 
2.9.3