[RFC v6 4/5] sched/fair: Provide arch hook to find domain for non idle core search scan

[Parth Shah <parth@linux.ibm.com>]

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@linux.ibm.com>
---
 kernel/sched/fair.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8643e6309451..af19e1f9d56d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5890,6 +5890,13 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 /* Define non-idle CPU as the one with the utilization >= 12.5% */
 #define merely_used_cpu(util) ((cpu_util(util)) > (100 >> 3))
 
+#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
+
 /*
  * Classify small background tasks with higher latency_nice value for task
  * packing.
@@ -5916,6 +5923,7 @@ static int select_non_idle_core(struct task_struct *p, int prev_cpu)
 	int iter_cpu, sibling;
 
 	cpumask_and(cpus, cpu_online_mask, p->cpus_ptr);
+	cpumask_and(cpus, cpus, arch_turbo_domain(prev_cpu));
 
 	for_each_cpu_wrap(iter_cpu, cpus, prev_cpu) {
 		int idle_cpu_count = 0, non_idle_cpu_count = 0;
-- 
2.17.2