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Message-Id: <20260206-feature-dynamic_isolcpus_dhei-v1-10-00a711eb0c74@gmail.com>
Date: Fri, 06 Feb 2026 02:04:31 -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 10/12] tick/nohz: Implement dynamic nohz_full state
update
The nohz_full state (tick_nohz_full_mask) is currently a boot-time
configuration that cannot be changed at runtime. This prevents
dynamic CPU isolation from being fully effective, as the scheduler tick
continues to run on newly isolated CPUs.
Remove the __init restriction from tick_nohz_full_setup() and
tick_nohz_init(). Implement a housekeeping notifier in the tick-sched
subsystem to handle HK_TYPE_TICK updates. When the mask is updated,
the new isolation mask is calculated and applied, and all online CPUs
are kicked to re-evaluate their tick dependency.
This allows the kernel to dynamically enter or exit full dynticks mode
on any CPU at runtime.
Signed-off-by: Qiliang Yuan <realwujing@...il.com>
Signed-off-by: Qiliang Yuan <yuanql9@...natelecom.cn>
---
include/linux/tick.h | 2 +-
kernel/time/tick-sched.c | 63 +++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 61 insertions(+), 4 deletions(-)
diff --git a/include/linux/tick.h b/include/linux/tick.h
index ac76ae9fa36d..40047523ec8c 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -271,7 +271,7 @@ static inline void tick_dep_clear_signal(struct signal_struct *signal,
extern void tick_nohz_full_kick_cpu(int cpu);
extern void __tick_nohz_task_switch(void);
-extern void __init tick_nohz_full_setup(cpumask_var_t cpumask);
+extern void tick_nohz_full_setup(cpumask_var_t cpumask);
#else
static inline bool tick_nohz_full_enabled(void) { return false; }
static inline bool tick_nohz_full_cpu(int cpu) { return false; }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 2f8a7923fa27..01d62dfc153f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -27,6 +27,7 @@
#include <linux/posix-timers.h>
#include <linux/context_tracking.h>
#include <linux/mm.h>
+#include <linux/sched/isolation.h>
#include <asm/irq_regs.h>
@@ -619,9 +620,14 @@ void __tick_nohz_task_switch(void)
}
/* Get the boot-time nohz CPU list from the kernel parameters. */
-void __init tick_nohz_full_setup(cpumask_var_t cpumask)
+void tick_nohz_full_setup(cpumask_var_t cpumask)
{
- alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
+ if (!tick_nohz_full_mask) {
+ if (system_state < SYSTEM_RUNNING)
+ alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
+ else
+ zalloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL);
+ }
cpumask_copy(tick_nohz_full_mask, cpumask);
tick_nohz_full_running = true;
}
@@ -643,10 +649,61 @@ static int tick_nohz_cpu_down(unsigned int cpu)
return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY;
}
-void __init tick_nohz_init(void)
+static int tick_nohz_housekeeping_reconfigure(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct housekeeping_update *upd = data;
+ int cpu;
+
+ if (action == HK_UPDATE_MASK && upd->type == HK_TYPE_TICK) {
+ cpumask_var_t non_housekeeping_mask;
+
+ if (!alloc_cpumask_var(&non_housekeeping_mask, GFP_KERNEL))
+ return NOTIFY_BAD;
+
+ cpumask_andnot(non_housekeeping_mask, cpu_possible_mask, upd->new_mask);
+
+ if (!tick_nohz_full_mask) {
+ if (!zalloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
+ free_cpumask_var(non_housekeeping_mask);
+ return NOTIFY_BAD;
+ }
+ }
+
+ /* Kick all CPUs to re-evaluate tick dependency before change */
+ for_each_online_cpu(cpu)
+ tick_nohz_full_kick_cpu(cpu);
+
+ cpumask_copy(tick_nohz_full_mask, non_housekeeping_mask);
+ tick_nohz_full_running = !cpumask_empty(tick_nohz_full_mask);
+
+ /* Kick all CPUs again to apply new nohz full state */
+ for_each_online_cpu(cpu)
+ tick_nohz_full_kick_cpu(cpu);
+
+ free_cpumask_var(non_housekeeping_mask);
+ }
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block tick_nohz_housekeeping_nb = {
+ .notifier_call = tick_nohz_housekeeping_reconfigure,
+};
+
+void tick_nohz_init(void)
{
int cpu, ret;
+ if (!tick_nohz_full_mask) {
+ if (system_state < SYSTEM_RUNNING)
+ alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
+ else
+ zalloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL);
+ }
+
+ housekeeping_register_notifier(&tick_nohz_housekeeping_nb);
+
if (!tick_nohz_full_running)
return;
--
2.51.0
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