[PATCH v6 2/6] timers: Add the available mask in timer migration

Gabriele Monaco
2025-05-30T14:21:29Z

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@redhat.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..25439f961ccf8 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 timer 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