Le Thu, Jun 26, 2025 at 01:48:55PM +0200, Gabriele Monaco a écrit :
> 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 2c2c8810b8137..2ec003c2bbbea 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_clear_cpu_available(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);
This is under the tmc lock.
>
> /*
> * CPU has to handle the local events on his own, when on the way to
> @@ -1459,7 +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);
But this is not.
We should make it clear what synchronizes the accesses to
tmigr_available_cpumask.
ie: we expect that either the cpu_hotplug_lock is write-held, or
it's read-held and cpuset_mutex is held.
But tmc->lock is not helpful. So the cpumask should be outside that
lock to avoid confusion.
Thanks.
> work_on_cpu(migrator, tmigr_trigger_active, NULL);
> }
>
> @@ -1480,6 +1484,7 @@ static int tmigr_set_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
>
--
Frederic Weisbecker
SUSE Labs