sched/deadline: Optimize dl_bw_cpus()

Return the weight of the root domain (rd) span in case it is a subset
of the cpu_active_mask.

Continue to compute the number of CPUs over rd span and cpu_active_mask
when in hotplug.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200520134243.19352-2-dietmar.eggemann@arm.com

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index f31964a..ec90265 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -54,10 +54,16 @@ static inline struct dl_bw *dl_bw_of(int i)
 static inline int dl_bw_cpus(int i)
 {
        struct root_domain *rd = cpu_rq(i)->rd;
-       int cpus = 0;
+       int cpus;
 
        RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
                         "sched RCU must be held");
+
+       if (cpumask_subset(rd->span, cpu_active_mask))
+               return cpumask_weight(rd->span);
+
+       cpus = 0;
+
        for_each_cpu_and(i, rd->span, cpu_active_mask)
                cpus++;