[RFC 06/11] sched/fair: Make select_idle_cpu() proportional to cores

[Peter Zijlstra]

Instead of calculating how many (logical) CPUs to scan, compute how
many cores to scan.

This changes behaviour for anything !SMT2.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
 kernel/sched/fair.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6352,6 +6352,8 @@ static int select_idle_smt(struct task_s
 
 #else /* CONFIG_SCHED_SMT */
 
+#define sched_smt_weight       1
+
 static inline int select_idle_core(struct task_struct *p, struct sched_domain 
*sd, int target)
 {
        return -1;
@@ -6381,6 +6383,8 @@ static int __select_idle_cpu(struct task
        return cpu;
 }
 
+#define sis_min_cores          2
+
 /*
  * Scan the LLC domain for idle CPUs; this is dynamically regulated by
  * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
@@ -6429,15 +6433,15 @@ static int select_idle_cpu(struct task_s
 
        if (sched_feat(SIS_PROP)) {
                u64 span_avg = sd->span_weight * avg_idle;
-               if (span_avg > 4*avg_cost)
+               if (span_avg > sis_min_cores * avg_cost)
                        nr = div_u64(span_avg, avg_cost);
                else
-                       nr = 4;
+                       nr = sis_min_cores;
        }
 
        time = local_clock();
 
-       cpu = __select_idle_cpu(p, sd, target, nr, &loops);
+       cpu = __select_idle_cpu(p, sd, target, nr * sched_smt_weight, &loops);
 
        time = local_clock() - time;