[PATCH] sched/fair: Add SMT4 group_smt_balance handling

[Shrikanth Hegde]

From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>

For SMT4, any group with more than 2 tasks will be marked as
group_smt_balance. Retain the behaviour of group_has_spare by marking
the busiest group as the group which has the least number of idle_cpus.

Also, handle rounding effect of adding (ncores_local + ncores_busy)
when the local is fully idle and busy group has more than 2 tasks.
Local group should try to pull at least 1 task in this case.

Originally-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxxxxxxx>
---
 kernel/sched/fair.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 932e7b78894a..9502013abe33 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9532,7 +9532,7 @@ static inline long sibling_imbalance(struct lb_env *env,
 	imbalance /= ncores_local + ncores_busiest;

 	/* Take advantage of resource in an empty sched group */
-	if (imbalance == 0 && local->sum_nr_running == 0 &&
+	if (imbalance <= 1 && local->sum_nr_running == 0 &&
 	    busiest->sum_nr_running > 1)
 		imbalance = 2;

@@ -9720,6 +9720,17 @@ static bool update_sd_pick_busiest(struct lb_env *env,
 		break;

 	case group_smt_balance:
+		/* no idle cpus on both groups handled by group_fully_busy below */
+		if (sgs->idle_cpus != 0 || busiest->idle_cpus != 0) {
+			if (sgs->idle_cpus > busiest->idle_cpus)
+				return false;
+			if (sgs->idle_cpus < busiest->idle_cpus)
+				return true;
+			if (sgs->sum_nr_running <= busiest->sum_nr_running)
+				return false;
+		}
+		break;
+
 	case group_fully_busy:
 		/*
 		 * Select the fully busy group with highest avg_load. In
--
2.31.1