On Thu, Jun 17, 2021 at 2:23 PM Nitesh Narayan Lal <nitesh@xxxxxxxxxx> wrote: > > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > 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_set_affinity_and_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. > > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx> > Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@xxxxxxxxx > --- > include/linux/interrupt.h | 41 ++++++++++++++++++++++++++++++++++++++- > kernel/irq/manage.c | 8 ++++---- > 2 files changed, 44 insertions(+), 5 deletions(-) > > diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h > index 2ed65b01c961..4ca491a76033 100644 > --- a/include/linux/interrupt.h > +++ b/include/linux/interrupt.h > @@ -328,7 +328,46 @@ extern int irq_force_affinity(unsigned int irq, const struct cpumask *cpumask); > 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, false); > +} > + > +/** > + * irq_set_affinity_and_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_set_affinity_and_hint(unsigned int irq, const struct cpumask *m) > +{ > + return __irq_apply_affinity_hint(irq, m, true); > +} > + > +/* > + * Deprecated. Use irq_update_affinity_hint() or irq_set_affinity_and_hint() > + * instead. > + */ > +static inline int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m) > +{ > + return irq_set_affinity_and_hint(irq, m); > +} > + > extern int irq_update_affinity_desc(unsigned int irq, > struct irq_affinity_desc *affinity); > > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > index ef30b4762947..837b63e63111 100644 > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -487,7 +487,8 @@ int irq_force_affinity(unsigned int irq, const struct cpumask *cpumask) > } > 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 irq, const struct cpumask *m) > 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) > { > -- > 2.27.0 > It turns out that this patch has an issue. The new interfaces are not added under the #ifdef (CONFIG_SMP)'s else section. I will fix it and send a v2 with other changes. -- Thanks Nitesh
