linux-kernel - [RFC PATCH v2 5/7] sched/fair: get rid of throttled_lb

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Message-Id: <20250409120746.635476-6-ziqianlu@bytedance.com>
Date: Wed,  9 Apr 2025 20:07:44 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: Valentin Schneider <vschneid@...hat.com>,
	Ben Segall <bsegall@...gle.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Don <joshdon@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Xi Wang <xii@...gle.com>
Cc: linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mel Gorman <mgorman@...e.de>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	Chuyi Zhou <zhouchuyi@...edance.com>,
	Jan Kiszka <jan.kiszka@...mens.com>
Subject: [RFC PATCH v2 5/7] 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>
---
 kernel/sched/fair.c | 33 +++------------------------------
 1 file changed, 3 insertions(+), 30 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 76b8a5ffcbdd2..ff4252995d677 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5808,23 +5808,6 @@ 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 !list_empty(&p->throttle_node);
@@ -6742,12 +6725,6 @@ 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) {}
@@ -9377,17 +9354,13 @@ 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.
+	 * 2) cannot be migrated to this CPU due to cpus_ptr, or
+	 * 3) running (obviously), or
+	 * 4) are cache-hot on their current CPU.
 	 */
 	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
-- 
2.39.5