linux-kernel - [RFCv3 7/8] sched/fair: Bound non idle core search within LLC domain

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Date:   Tue, 25 Jun 2019 10:07:25 +0530
From:   Parth Shah <parth@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, dietmar.eggemann@....com,
        patrick.bellasi@....com
Subject: [RFCv3 7/8] sched/fair: Bound non idle core search within LLC domain

This patch specifies the method which returns sched domain to limit the
search for a non idle core. By default, limit the search in LLC domain
which usually includes all the cores across the system.

The select_non_idle_core searches for the non idle cores across whole
system. 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 | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9d11631ce18c..b049c9d73f1d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5973,6 +5973,13 @@ static inline bool core_underutilized(unsigned long core_util,
 	return core_util < (core_capacity >> UNDERUTILIZED_THRESHOLD);
 }
 
+#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
+
 /*
  * Try to find a non idle core in the system  with spare capacity
  * available for task packing, thereby keeping minimal cores active.
@@ -5983,7 +5990,8 @@ 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) {
 		unsigned long core_util = 0;
-- 
2.17.1