[PATCH v4 05/12] sched/fair: Keep a fully_busy SMT sched group as busiest

From: Ricardo Neri
Date: Thu Apr 06 2023 - 16:21:20 EST


When comparing two fully_busy scheduling groups, keep the current busiest
group if it represents an SMT core. Tasks in such scheduling group share
CPU resources and need more help than tasks in a non-SMT fully_busy group.

Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Ionela Voinescu <ionela.voinescu@xxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Tested-by: Zhang Rui <rui.zhang@xxxxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
Changes since v3:
* None

Changes since v2:
* Introduced this patch.

Changes since v1:
* N/A
---
kernel/sched/fair.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b151e93ec316..ea23a5163bfa 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9566,10 +9566,22 @@ static bool update_sd_pick_busiest(struct lb_env *env,
* contention when accessing shared HW resources.
*
* XXX for now avg_load is not computed and always 0 so we
- * select the 1st one.
+ * select the 1st one, except if @sg is composed of SMT
+ * siblings.
*/
- if (sgs->avg_load <= busiest->avg_load)
+
+ if (sgs->avg_load < busiest->avg_load)
return false;
+
+ if (sgs->avg_load == busiest->avg_load) {
+ /*
+ * SMT sched groups need more help than non-SMT groups.
+ * If @sg happens to also be SMT, either choice is good.
+ */
+ if (sds->busiest->flags & SD_SHARE_CPUCAPACITY)
+ return false;
+ }
+
break;

case group_has_spare:
--
2.25.1