linux-kernel - [tip: sched/core] sched/fair: Get rid of throttled_lb

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Message-ID: <175688670583.1920.14676738682642599307.tip-bot2@tip-bot2>
Date: Wed, 03 Sep 2025 08:05:05 -0000
From: "tip-bot2 for Aaron Lu" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: K Prateek Nayak <kprateek.nayak@....com>,
 Aaron Lu <ziqianlu@...edance.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Valentin Schneider <vschneid@...hat.com>,
 Matteo Martelli <matteo.martelli@...ethink.co.uk>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/fair: Get rid of throttled_lb_pair()

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     5b726e9bf9544a349090879a513a5e00da486c14
Gitweb:        https://git.kernel.org/tip/5b726e9bf9544a349090879a513a5e00da486c14
Author:        Aaron Lu <ziqianlu@...edance.com>
AuthorDate:    Fri, 29 Aug 2025 16:11:20 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 03 Sep 2025 10:03:14 +02:00

sched/fair: Get rid of throttled_lb_pair()

Now that throttled tasks are dequeued and can not stay on rq's cfs_tasks
list, there is no need to take special care of these throttled tasks
anymore in load balance.

Suggested-by: K Prateek Nayak <kprateek.nayak@....com>
Signed-off-by: Aaron Lu <ziqianlu@...edance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Valentin Schneider <vschneid@...hat.com>
Tested-by: Matteo Martelli <matteo.martelli@...ethink.co.uk>
Tested-by: K Prateek Nayak <kprateek.nayak@....com>
Link: https://lore.kernel.org/r/20250829081120.806-6-ziqianlu@bytedance.com
---
 kernel/sched/fair.c | 35 ++++-------------------------------
 1 file changed, 4 insertions(+), 31 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bdc9bfa..df8dc38 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5735,23 +5735,6 @@ static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
 	return cfs_bandwidth_used() && cfs_rq->throttle_count;
 }
 
-/*
- * Ensure that neither of the group entities corresponding to src_cpu or
- * dest_cpu are members of a throttled hierarchy when performing group
- * load-balance operations.
- */
-static inline int throttled_lb_pair(struct task_group *tg,
-				    int src_cpu, int dest_cpu)
-{
-	struct cfs_rq *src_cfs_rq, *dest_cfs_rq;
-
-	src_cfs_rq = tg->cfs_rq[src_cpu];
-	dest_cfs_rq = tg->cfs_rq[dest_cpu];
-
-	return throttled_hierarchy(src_cfs_rq) ||
-	       throttled_hierarchy(dest_cfs_rq);
-}
-
 static inline bool task_is_throttled(struct task_struct *p)
 {
 	return cfs_bandwidth_used() && p->throttled;
@@ -6743,12 +6726,6 @@ static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
 	return 0;
 }
 
-static inline int throttled_lb_pair(struct task_group *tg,
-				    int src_cpu, int dest_cpu)
-{
-	return 0;
-}
-
 #ifdef CONFIG_FAIR_GROUP_SCHED
 void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth *parent) {}
 static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
@@ -9385,18 +9362,14 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 	/*
 	 * We do not migrate tasks that are:
 	 * 1) delayed dequeued unless we migrate load, or
-	 * 2) throttled_lb_pair, or
-	 * 3) cannot be migrated to this CPU due to cpus_ptr, or
-	 * 4) running (obviously), or
-	 * 5) are cache-hot on their current CPU, or
-	 * 6) are blocked on mutexes (if SCHED_PROXY_EXEC is enabled)
+	 * 2) cannot be migrated to this CPU due to cpus_ptr, or
+	 * 3) running (obviously), or
+	 * 4) are cache-hot on their current CPU, or
+	 * 5) are blocked on mutexes (if SCHED_PROXY_EXEC is enabled)
 	 */
 	if ((p->se.sched_delayed) && (env->migration_type != migrate_load))
 		return 0;
 
-	if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
-		return 0;
-
 	/*
 	 * We want to prioritize the migration of eligible tasks.
 	 * For ineligible tasks we soft-limit them and only allow