linux-kernel - [PATCH RFC 12/12] sched/isolation: Bridge isolcpus and support runtime tick offload init

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Message-Id: <20260206-feature-dynamic_isolcpus_dhei-v1-12-00a711eb0c74@gmail.com>
Date: Fri, 06 Feb 2026 02:04:33 -0500
From: Qiliang Yuan <realwujing@...il.com>
To: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
 Juri Lelli <juri.lelli@...hat.com>, 
 Vincent Guittot <vincent.guittot@...aro.org>, 
 Dietmar Eggemann <dietmar.eggemann@....com>, 
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, 
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, 
 Thomas Gleixner <tglx@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>, 
 Joel Fernandes <joelagnelf@...dia.com>, 
 Josh Triplett <josh@...htriplett.org>, Boqun Feng <boqun.feng@...il.com>, 
 Uladzislau Rezki <urezki@...il.com>, 
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
 Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang@...ux.dev>, 
 Tejun Heo <tj@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
 Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>, 
 Michal Hocko <mhocko@...e.com>, Brendan Jackman <jackmanb@...gle.com>, 
 Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org, linux-mm@...ck.org, 
 Qiliang Yuan <realwujing@...il.com>, Qiliang Yuan <yuanql9@...natelecom.cn>
Subject: [PATCH RFC 12/12] sched/isolation: Bridge isolcpus and support
 runtime tick offload init

Bridge the boot-time 'isolcpus' and 'nohz_full' parameters with the
DHEI sysfs interface. Ensure that housekeeping_init() correctly
initializes the isolation state and that subsequent sysfs updates
can take over management even if no isolation was configured at boot.

Remove __init from sched_tick_offload_init() and update it to be
safe for multiple calls. This allows DHEI to initialize tick offload
infrastructure at runtime when the first tick-isolated core is
configured.

Signed-off-by: Qiliang Yuan <realwujing@...il.com>
Signed-off-by: Qiliang Yuan <yuanql9@...natelecom.cn>
---
 kernel/sched/core.c      | 5 ++++-
 kernel/sched/isolation.c | 3 +++
 kernel/sched/sched.h     | 2 +-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 045f83ad261e..d155e1132d6b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5685,8 +5685,11 @@ static void sched_tick_stop(int cpu)
 }
 #endif /* CONFIG_HOTPLUG_CPU */

-int __init sched_tick_offload_init(void)
+int sched_tick_offload_init(void)
 {
+	if (tick_work_cpu)
+		return 0;
+
 	tick_work_cpu = alloc_percpu(struct tick_work);
 	BUG_ON(!tick_work_cpu);
 	return 0;
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 30798e790b9f..76c039a01fb0 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -241,6 +241,9 @@ static ssize_t housekeeping_store(struct kobject *kobject,
 	housekeeping.flags |= BIT(type);
 	static_branch_enable(&housekeeping_overridden);

+	if (type == HK_TYPE_TICK || type == HK_TYPE_TIMER || type == HK_TYPE_RCU)
+		sched_tick_offload_init();
+
 	housekeeping_update_notify(type, new_mask);

 	err = count;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 93fce4bbff5e..0079e7210c38 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2867,7 +2867,7 @@ extern void post_init_entity_util_avg(struct task_struct *p);

 #ifdef CONFIG_NO_HZ_FULL
 extern bool sched_can_stop_tick(struct rq *rq);
-extern int __init sched_tick_offload_init(void);
+extern int sched_tick_offload_init(void);

 /*
  * Tick may be needed by tasks in the runqueue depending on their policy and

-- 
2.51.0