Re: [PATCH v2 15/25] genirq: Update request_percpu_nmi() to take an affinity

Jonathan Cameron
2025-09-16T16:19:47Z

On Mon, 15 Sep 2025 09:56:52 +0100
Marc Zyngier <maz@kernel.org> wrote:

> Continue spreading the notion of affinity to the percpu interrupt
> request code by updating the call sites that use request_percpu_nmi()
> (all two of them) to take an affinity pointer. This pointer is
> firmly NULL for now.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
A few fussy reviewer comments inline.

> ---
> arch/arm64/kernel/smp.c | 2 +-
> drivers/perf/arm_pmu.c | 4 +++-
> include/linux/interrupt.h | 4 ++--
> kernel/irq/manage.c | 11 +++++++----
> 4 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 68cea3a4a35ca..6fb838eee2e7d 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -1094,7 +1094,7 @@ static void ipi_setup_sgi(int ipi)
> irq = ipi_irq_base + ipi;
>
> if (ipi_should_be_nmi(ipi)) {
> - err = request_percpu_nmi(irq, ipi_handler, "IPI", &irq_stat);
> + err = request_percpu_nmi(irq, ipi_handler, "IPI", NULL, &irq_stat);
> WARN(err, "Could not request IRQ %d as NMI, err=%d\n", irq, err);
> } else {
> err = request_percpu_irq(irq, ipi_handler, "IPI", &irq_stat);
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 5c310e803dd78..de9eca2290a97 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -659,7 +659,9 @@ int armpmu_request_irq(int irq, int cpu)
> irq_ops = &pmunmi_ops;
> }
> } else if (armpmu_count_irq_users(irq) == 0) {
> - err = request_percpu_nmi(irq, handler, "arm-pmu", &cpu_armpmu);
> + err = request_percpu_nmi(irq, handler, "arm-pmu",
> + NULL,

I was assuming this odd formatting was to help reduce churn in a later patch, but nope
this whole block get replaced in patch 18. So might as well move NULL up a line
an have a cleaner intermediate state.

> + &cpu_armpmu);
>
> /* If cannot get an NMI, get a normal interrupt */
> if (err) {
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 52147d5f432b3..2134e7c08c169 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -197,8 +197,8 @@ request_percpu_irq(unsigned int irq, irq_handler_t handler,
> }
>
> extern int __must_check
> -request_percpu_nmi(unsigned int irq, irq_handler_t handler,
> - const char *devname, void __percpu *dev);
> +request_percpu_nmi(unsigned int irq, irq_handler_t handler, const char *devname,
Odd inconsistency in parameter naming devname/name

Perhaps worth tidying that up whilst here. I only noticed because of the
wrap comment below.

> + const struct cpumask *affinity, void __percpu *dev_id);
>
> extern const void *free_irq(unsigned int, void *);
> extern void free_percpu_irq(unsigned int, void __percpu *);
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 5f4c651677436..49c237aca2a70 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -2527,6 +2527,7 @@ EXPORT_SYMBOL_GPL(__request_percpu_irq);
> * @irq: Interrupt line to allocate
> * @handler: Function to be called when the IRQ occurs.
> * @name: An ascii name for the claiming device
> + * @affinity: A cpumask describing the target CPUs for this interrupt
> * @dev_id: A percpu cookie passed back to the handler function
> *
> * This call allocates interrupt resources for a per CPU NMI. Per CPU NMIs
> @@ -2544,7 +2545,8 @@ EXPORT_SYMBOL_GPL(__request_percpu_irq);
> * will fail returning a negative value.
> */
> int request_percpu_nmi(unsigned int irq, irq_handler_t handler,
> - const char *name, void __percpu *dev_id)
> + const char *name,
> + const struct cpumask *affinity, void __percpu *dev_id)

This seems like an odd wrap and I can't immediately see it making more sense
in later patches.

> {

>