linux-kernel - [RFC][PATCH 03/10] sched/fair: Cleanup pick_task

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Date: Fri, 05 Apr 2024 12:27:57 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...hat.com,
 peterz@...radead.org,
 juri.lelli@...hat.com,
 vincent.guittot@...aro.org,
 dietmar.eggemann@....com,
 rostedt@...dmis.org,
 bsegall@...gle.com,
 mgorman@...e.de,
 bristot@...hat.com,
 vschneid@...hat.com,
 linux-kernel@...r.kernel.org
Cc: kprateek.nayak@....com,
 wuyun.abel@...edance.com,
 tglx@...utronix.de,
 efault@....de
Subject: [RFC][PATCH 03/10] sched/fair: Cleanup pick_task_fair() vs throttle

Per 54d27365cae8 ("sched/fair: Prevent throttling in early
pick_next_task_fair()") the reason check_cfs_rq_runtime() is under the
'if (curr)' check is to ensure the (downward) traversal does not
result in an empty cfs_rq.

But then the pick_task_fair() 'copy' of all this made it restart the
traversal anyway, so that seems to solve the issue too.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/fair.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8435,11 +8435,11 @@ static struct task_struct *pick_task_fai
 				update_curr(cfs_rq);
 			else
 				curr = NULL;
-
-			if (unlikely(check_cfs_rq_runtime(cfs_rq)))
-				goto again;
 		}
 
+		if (unlikely(check_cfs_rq_runtime(cfs_rq)))
+			goto again;
+
 		se = pick_next_entity(cfs_rq);
 		cfs_rq = group_cfs_rq(se);
 	} while (cfs_rq);