linux-kernel - [PATCH] sched: remove HZ

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Date: Wed, 15 May 2024 09:37:05 -0400
From: Phil Auld <pauld@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Ben Segall <bsegall@...gle.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>
Subject: [PATCH] sched: remove HZ_BW feature hedge

As a hedge against unexpected user issues commit 88c56cfeaec4
("sched/fair: Block nohz tick_stop when cfs bandwidth in use")
included a scheduler feature to disable the new functionality.
It's been a few releases (v6.6) and no screams, so remove it.

Signed-off-by: Phil Auld <pauld@...hat.com>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Valentin Schneider <vschneid@...hat.com>
---
 kernel/sched/core.c     | 2 +-
 kernel/sched/fair.c     | 2 +-
 kernel/sched/features.h | 2 --
 3 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7019a40457a6..d7afcee8e2ae 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1269,7 +1269,7 @@ bool sched_can_stop_tick(struct rq *rq)
 	 * dequeued by migrating while the constrained task continues to run.
 	 * E.g. going from 2->1 without going through pick_next_task().
 	 */
-	if (sched_feat(HZ_BW) && __need_bw_check(rq, rq->curr)) {
+	if (__need_bw_check(rq, rq->curr)) {
 		if (cfs_task_bw_constrained(rq->curr))
 			return false;
 	}
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c62805dbd608..06e026f10cb4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6549,7 +6549,7 @@ static void sched_fair_update_stop_tick(struct rq *rq, struct task_struct *p)
 {
 	int cpu = cpu_of(rq);
 
-	if (!sched_feat(HZ_BW) || !cfs_bandwidth_used())
+	if (!cfs_bandwidth_used())
 		return;
 
 	if (!tick_nohz_full_cpu(cpu))
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 143f55df890b..929021fd6bc4 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -85,5 +85,3 @@ SCHED_FEAT(WA_BIAS, true)
 SCHED_FEAT(UTIL_EST, true)
 
 SCHED_FEAT(LATENCY_WARN, false)
-
-SCHED_FEAT(HZ_BW, true)
-- 
2.39.3