| Message ID | 20220616064028.57933-5-samuel@sholland.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | genirq/irqchip: RISC-V PLIC cleanup and optimization | expand |
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.
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
On Tue, 21 Jun 2022 05:03:43 +0100, Samuel Holland <samuel@sholland.org> wrote: > > 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. Ah, indeed. Not going to work very well... > 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). Sounds like a plan. Thanks, M.
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 } static inline struct cpumask *irq_get_affinity_mask(int irq)
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(+)