sched/fair: Move avg_scan_cost calculations under SIS_PROP

As noted by Vincent Guittot, avg_scan_costs are calculated for SIS_PROP
even if SIS_PROP is disabled. Move the time calculations under a SIS_PROP
check and while we are at it, exclude the cost of initialising the CPU
mask from the average scan cost.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210125085909.4600-3-mgorman@techsingularity.net

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 124cb6e..4c18ef6 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6166,6 +6166,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
        if (!this_sd)
                return -1;
 
+       cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+
        if (sched_feat(SIS_PROP)) {
                u64 avg_cost, avg_idle, span_avg;
 
@@ -6181,11 +6183,9 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
                        nr = div_u64(span_avg, avg_cost);
                else
                        nr = 4;
-       }
-
-       time = cpu_clock(this);
 
-       cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
+               time = cpu_clock(this);
+       }
 
        for_each_cpu_wrap(cpu, cpus, target) {
                if (!--nr)
@@ -6194,8 +6194,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
                        break;
        }
 
-       time = cpu_clock(this) - time;
-       update_avg(&this_sd->avg_scan_cost, time);
+       if (sched_feat(SIS_PROP)) {
+               time = cpu_clock(this) - time;
+               update_avg(&this_sd->avg_scan_cost, time);
+       }
 
        return cpu;
 }