linux-kernel - [PATCH v2 2/3] timers: Add the available mask in timer migration

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Message-ID: <20250415102500.100415-7-gmonaco@redhat.com>
Date: Tue, 15 Apr 2025 12:25:03 +0200
From: Gabriele Monaco <gmonaco@...hat.com>
To: linux-kernel@...r.kernel.org,
	Frederic Weisbecker <frederic@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <longman@...hat.com>
Cc: Gabriele Monaco <gmonaco@...hat.com>
Subject: [PATCH v2 2/3] timers: Add the available mask in timer migration

Keep track of the CPUs available for timer migration in a cpumask. This
prepares the ground to generalise the concept of unavailable CPUs.

Signed-off-by: Gabriele Monaco <gmonaco@...hat.com>
---
 kernel/time/timer_migration.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index 7efd897c79599..1fae38fbac8c2 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -422,6 +422,9 @@ static unsigned int tmigr_crossnode_level __read_mostly;
 
 static DEFINE_PER_CPU(struct tmigr_cpu, tmigr_cpu);
 
+/* CPUs available for migration */
+static cpumask_var_t tmigr_available_cpumask;
+
 #define TMIGR_NONE	0xFF
 #define BIT_CNT		8
 
@@ -1449,6 +1452,7 @@ static int tmigr_cpu_unavailable(unsigned int cpu)
 	raw_spin_lock_irq(&tmc->lock);
 	tmc->available = false;
 	WRITE_ONCE(tmc->wakeup, KTIME_MAX);
+	cpumask_clear_cpu(cpu, tmigr_available_cpumask);
 
 	/*
 	 * CPU has to handle the local events on his own, when on the way to
@@ -1459,7 +1463,7 @@ static int tmigr_cpu_unavailable(unsigned int cpu)
 	raw_spin_unlock_irq(&tmc->lock);
 
 	if (firstexp != KTIME_MAX) {
-		migrator = cpumask_any_but(cpu_online_mask, cpu);
+		migrator = cpumask_any(tmigr_available_cpumask);
 		work_on_cpu(migrator, tmigr_trigger_active, NULL);
 	}
 
@@ -1480,6 +1484,7 @@ static int tmigr_cpu_available(unsigned int cpu)
 	if (!tmc->idle)
 		__tmigr_cpu_activate(tmc);
 	tmc->available = true;
+	cpumask_set_cpu(cpu, tmigr_available_cpumask);
 	raw_spin_unlock_irq(&tmc->lock);
 	return 0;
 }
@@ -1801,6 +1806,11 @@ static int __init tmigr_init(void)
 	if (ncpus == 1)
 		return 0;
 
+	if (!zalloc_cpumask_var(&tmigr_available_cpumask, GFP_KERNEL)) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
 	/*
 	 * Calculate the required hierarchy levels. Unfortunately there is no
 	 * reliable information available, unless all possible CPUs have been
-- 
2.49.0