Messages in this thread | | | Date | Sat, 18 Jun 2022 10:01:55 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH v2 4/6] genirq: Provide an IRQ affinity mask in non-SMP configs |
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Hi Samuel,
On Thu, 16 Jun 2022 07:40:26 +0100, Samuel Holland <samuel@sholland.org> wrote: > > IRQ affinity masks are not allocated in uniprocessor configurations. > This requires special case non-SMP code in drivers for irqchips which > have per-CPU enable or mask registers. > > Since IRQ affinity is always the same in a uniprocessor configuration, > we can still provide the correct affinity mask without allocating one > per IRQ. We can reuse the system-wide cpu_possible_mask. > > By returning a real cpumask from irq_data_get_affinity_mask even when > SMP is disabled, irqchip drivers which iterate over that mask will > automatically do the right thing. > > Signed-off-by: Samuel Holland <samuel@sholland.org> > --- > > (no changes since v1) > > include/linux/irq.h | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/include/linux/irq.h b/include/linux/irq.h > index 69ee4e2f36ce..d5e958b026aa 100644 > --- a/include/linux/irq.h > +++ b/include/linux/irq.h > @@ -151,7 +151,9 @@ struct irq_common_data { > #endif > void *handler_data; > struct msi_desc *msi_desc; > +#ifdef CONFIG_SMP > cpumask_var_t affinity; > +#endif > #ifdef CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK > cpumask_var_t effective_affinity; > #endif > @@ -881,7 +883,11 @@ static inline int irq_data_get_node(struct irq_data *d) > > static inline struct cpumask *irq_data_get_affinity_mask(struct irq_data *d) > { > +#ifdef CONFIG_SMP > return d->common->affinity; > +#else > + return &__cpu_possible_mask; > +#endif
I have a bad feeling about this one. Being in a !SMP configuration doesn't necessarily mean that __cpu_possible_mask only contains a single CPU, specially with things like CONFIG_INIT_ALL_POSSIBLE. I can also imagine an architecture populating this bitmap from firmware tables irrespective of the SMP status of the kernel.
Can't you use something like:
return cpumask_of(0);
which is guaranteed to be the right thing on !SMP configuration?
Thanks,
M.
-- Without deviation from the norm, progress is not possible.
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