sched: Store system-wide maximum cpu capacity in root domain

To be able to compare the capacity of the target cpu with the highest
cpu capacity of the system in the wakeup path, store the system-wide
maximum cpu capacity in the root domain.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

kernel/sched/core.c

@@ -6975,6 +6975,7 @@ static int build_sched_domains(const struct cpumask *cpu_map,
 	enum s_alloc alloc_state;
 	struct sched_domain *sd;
 	struct s_data d;
+	struct rq *rq = NULL;
 	int i, ret = -ENOMEM;
 
 	alloc_state = __visit_domain_allocation_hell(&d, cpu_map);
@@ -7025,11 +7026,18 @@ static int build_sched_domains(const struct cpumask *cpu_map,
 	/* Attach the domains */
 	rcu_read_lock();
 	for_each_cpu(i, cpu_map) {
+		rq = cpu_rq(i);
 		sd = *per_cpu_ptr(d.sd, i);
 		cpu_attach_domain(sd, d.rd, i);
+
+		if (rq->cpu_capacity_orig > rq->rd->max_cpu_capacity)
+			rq->rd->max_cpu_capacity = rq->cpu_capacity_orig;
 	}
 	rcu_read_unlock();
 
+	if (rq)
+		pr_info("max cpu_capacity %lu\n", rq->rd->max_cpu_capacity);
+
 	ret = 0;
 error:
 	__free_domain_allocs(&d, alloc_state, cpu_map);

kernel/sched/sched.h

@@ -543,6 +543,9 @@ struct root_domain {
 	 */
 	cpumask_var_t rto_mask;
 	struct cpupri cpupri;
+
+	/* Maximum cpu capacity in the system. */
+	unsigned long max_cpu_capacity;
 };
 
 extern struct root_domain def_root_domain;