From: Pat Somaru <patso@likewhatevs.io>
Date: Fri, 20 Sep 2024 19:41:59 +0000 (-0400)
Subject: sched, sched_ext: Disable SM_IDLE/rq empty path when scx_enabled()
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=edf1c586e92675c4e0eb27758fcdb55a56838de1;p=users%2Fjedix%2Flinux-maple.git

sched, sched_ext: Disable SM_IDLE/rq empty path when scx_enabled()

Disable the rq empty path when scx is enabled. SCX must consult the BPF
scheduler (via the dispatch path in balance) to determine if rq is empty.

This fixes stalls when scx is enabled.

Signed-off-by: Pat Somaru <patso@likewhatevs.io>
Fixes: 3dcac251b066 ("sched/core: Introduce SM_IDLE and an idle re-entry fast-path in __schedule()")
Signed-off-by: Tejun Heo <tj@kernel.org>
---

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b6cc1cf499d6..43e453ab7e20 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6591,7 +6591,8 @@ static void __sched notrace __schedule(int sched_mode)
 	 */
 	prev_state = READ_ONCE(prev->__state);
 	if (sched_mode == SM_IDLE) {
-		if (!rq->nr_running) {
+		/* SCX must consult the BPF scheduler to tell if rq is empty */
+		if (!rq->nr_running && !scx_enabled()) {
 			next = prev;
 			goto picked;
 		}