linux-kernel - [RFC v5 5/6] sched/fair: Provide arch hook to find domain for non idle core search scan

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Date:   Mon,  7 Oct 2019 14:00:50 +0530
From:   Parth Shah <parth@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, patrick.bellasi@...bug.net,
        valentin.schneider@....com, pavel@....cz, dsmythies@...us.net,
        quentin.perret@....com, rafael.j.wysocki@...el.com,
        tim.c.chen@...ux.intel.com, daniel.lezcano@...aro.org
Subject: [RFC v5 5/6] sched/fair: Provide arch hook to find domain for non idle core search scan

Specify the method which returns cpumask within which to limit the
search for a non idle core. By default, limit the search in LLC domain
which usually includes few/all the cores in the processor chip.

The select_non_idle_core searches for the non idle cores in the LLC domain.
But in the systems with multiple NUMA domains, the Turbo frequency can be
sustained within the NUMA domain without being affected from other
NUMA. For such case, arch_turbo_domain can be tuned to change domain for
non idle core search.

Signed-off-by: Parth Shah <parth@...ux.ibm.com>
---
 kernel/sched/fair.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4a1b6474338..731d1aaa6bc0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5967,6 +5967,14 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 }
 
 #ifdef CONFIG_SCHED_SMT
+
+#ifndef arch_turbo_domain
+static __always_inline struct cpumask *arch_turbo_domain(int cpu)
+{
+	return sched_domain_span(rcu_dereference(per_cpu(sd_llc, cpu)));
+}
+#endif
+
 static inline bool is_background_task(struct task_struct *p)
 {
 	if (p->flags & PF_CAN_BE_PACKED)
@@ -5991,7 +5999,8 @@ static int select_non_idle_core(struct task_struct *p, int prev_cpu, int target)
 	struct cpumask *cpus = this_cpu_cpumask_var_ptr(turbo_sched_mask);
 	int iter_cpu, sibling;
 
-	cpumask_and(cpus, cpu_online_mask, p->cpus_ptr);
+	cpumask_and(cpus, cpu_online_mask, arch_turbo_domain(prev_cpu));
+	cpumask_and(cpus, cpus, p->cpus_ptr);
 
 	for_each_cpu_wrap(iter_cpu, cpus, prev_cpu) {
 		int idle_cpu_count = 0, non_idle_cpu_count = 0;
-- 
2.17.1