[RESEND PATCH v13 3/9] timers: Add the available mask in timer migration

Gabriele Monaco
2025-10-20T11:28:21Z

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

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
---
kernel/time/timer_migration.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index 55b186fd146c..865071ab5062 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -422,6 +422,12 @@ static unsigned int tmigr_crossnode_level __read_mostly;

static DEFINE_PER_CPU(struct tmigr_cpu, tmigr_cpu);

+/*
+ * CPUs available for timer migration.
+ * Protected by cpuset_mutex (with cpus_read_lock held) or cpus_write_lock.
+ */
+static cpumask_var_t tmigr_available_cpumask;
+
#define TMIGR_NONE 0xFF
#define BIT_CNT 8

@@ -1443,6 +1449,7 @@ static int tmigr_clear_cpu_available(unsigned int cpu)
int migrator;
u64 firstexp;

+ cpumask_clear_cpu(cpu, tmigr_available_cpumask);
raw_spin_lock_irq(&tmc->lock);
tmc->available = false;
WRITE_ONCE(tmc->wakeup, KTIME_MAX);
@@ -1456,7 +1463,7 @@ static int tmigr_clear_cpu_available(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);
}

@@ -1471,6 +1478,7 @@ static int tmigr_set_cpu_available(unsigned int cpu)
if (WARN_ON_ONCE(!tmc->tmgroup))
return -EINVAL;

+ cpumask_set_cpu(cpu, tmigr_available_cpumask);
raw_spin_lock_irq(&tmc->lock);
trace_tmigr_cpu_available(tmc);
tmc->idle = timer_base_is_idle();
@@ -1808,6 +1816,11 @@ 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
--
2.51.0