Hi,
On Fri, May 21, 2021 at 02:03:06PM +0200, Thomas Gleixner wrote:
> The discussion about removing the side effect of irq_set_affinity_hint() of
> actually applying the cpumask (if not NULL) as affinity to the interrupt,
> unearthed a few unpleasantries:
>
> 1) The modular perf drivers rely on the current behaviour for the very
> wrong reasons.
>
> 2) While none of the other drivers prevents user space from changing
> the affinity, a cursorily inspection shows that there are at least
> expectations in some drivers.
>
> #1 needs to be cleaned up anyway, so that's not a problem
>
> #2 might result in subtle regressions especially when irqbalanced (which
> nowadays ignores the affinity hint) is disabled.
>
> Provide new interfaces:
>
> irq_update_affinity_hint() - Only sets the affinity hint pointer
> irq_apply_affinity_hint() - Set the pointer and apply the affinity to
> the interrupt
>
> Make irq_set_affinity_hint() a wrapper around irq_apply_affinity_hint() and
> document it to be phased out.
Is there recommended way to retrieve the CPU number that the interrupt has
affinity?
Previously a driver (I'm looking at drivers/net/ethernet/amazon/ena) that
uses irq_set_affinity_hint() to spread out IRQ knows the corresponding CPU
number since they're using their own spreading scheme. Now, phasing out
irq_set_affinity_hint(), and thus relying on request_irq() to spread the
load instead, there don't seem to be a easy way to get the CPU number.
In theory the following could work, but including irq.h does not look like a
good idea given that the comment in its explicitly ask not to be included in
generic code.
#include <linux/irq.h>
int irq = request_irq(...);
struct irq_data *data = irq_get_irq_data(irq);
struct cpumask *mask = irq_data_get_effective_affinity_mask(data);
int cpu = cpumask_first(mask);
Any suggestions?
Thanks,
Shung-Hsi
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@xxxxxxxxx
> ---
> Applies on:
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git irq/core
> ---
> include/linux/interrupt.h | 41 ++++++++++++++++++++++++++++++++++++++++-
> kernel/irq/manage.c | 8 ++++----
> 2 files changed, 44 insertions(+), 5 deletions(-)
>
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -328,7 +328,46 @@ extern int irq_force_affinity(unsigned i
> extern int irq_can_set_affinity(unsigned int irq);
> extern int irq_select_affinity(unsigned int irq);
>
> -extern int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m);
> +extern int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,
> + bool setaffinity);
> +
> +/**
> + * irq_update_affinity_hint - Update the affinity hint
> + * @irq: Interrupt to update
> + * @cpumask: cpumask pointer (NULL to clear the hint)
> + *
> + * Updates the affinity hint, but does not change the affinity of the interrupt.
> + */
> +static inline int
> +irq_update_affinity_hint(unsigned int irq, const struct cpumask *m)
> +{
> + return __irq_apply_affinity_hint(irq, m, true);
> +}
> +
> +/**
> + * irq_apply_affinity_hint - Update the affinity hint and apply the provided
> + * cpumask to the interrupt
> + * @irq: Interrupt to update
> + * @cpumask: cpumask pointer (NULL to clear the hint)
> + *
> + * Updates the affinity hint and if @cpumask is not NULL it applies it as
> + * the affinity of that interrupt.
> + */
> +static inline int
> +irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m)
> +{
> + return __irq_apply_affinity_hint(irq, m, true);
> +}
> +
> +/*
> + * Deprecated. Use irq_update_affinity_hint() or irq_apply_affinity_hint()
> + * instead.
> + */
> +static inline int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
> +{
> + return irq_apply_affinity_hint(irq, cpumask);
> +}
> +
> extern int irq_update_affinity_desc(unsigned int irq,
> struct irq_affinity_desc *affinity);
>
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -487,7 +487,8 @@ int irq_force_affinity(unsigned int irq,
> }
> EXPORT_SYMBOL_GPL(irq_force_affinity);
>
> -int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
> +int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,
> + bool setaffinity)
> {
> unsigned long flags;
> struct irq_desc *desc = irq_get_desc_lock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
> @@ -496,12 +497,11 @@ int irq_set_affinity_hint(unsigned int i
> return -EINVAL;
> desc->affinity_hint = m;
> irq_put_desc_unlock(desc, flags);
> - /* set the initial affinity to prevent every interrupt being on CPU0 */
> - if (m)
> + if (m && setaffinity)
> __irq_set_affinity(irq, m, false);
> return 0;
> }
> -EXPORT_SYMBOL_GPL(irq_set_affinity_hint);
> +EXPORT_SYMBOL_GPL(__irq_apply_affinity_hint);
>
> static void irq_affinity_notify(struct work_struct *work)
> {
