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

[Peter Zijlstra <peterz@infradead.org>]

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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) <peterz@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;