Messages in this thread | | | Subject | Re: [PATCH v2 4/6] genirq: Provide an IRQ affinity mask in non-SMP configs | From | Samuel Holland <> | Date | Mon, 20 Jun 2022 23:03:43 -0500 |
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On 6/18/22 4:01 AM, Marc Zyngier wrote: > 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?
I can if I cast away the const. However I see a lot of:
cpumask_copy(irq_data_get_affinity_mask(d), foo);
which I suppose is a great reason not to do what I am doing. The right solution seems to be adding irq_data_update_affinity() to match irq_data_update_effective_affinity(), and making both getters return a const cpumask. Then I can use cpumask_of(0).
Regards, Samuel
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