Re: [PATCH] genirq: Provide new interfaces for affinity hints

[Nitesh Lal <nilal@redhat.com>]

On Mon, Jun 7, 2021 at 1:00 PM Nitesh Lal <nilal@redhat.com> wrote:
>
> On Fri, May 21, 2021 at 8:03 AM Thomas Gleixner <tglx@linutronix.de> 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.
> >
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@intel.com
> > ---
> > 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);
>
> Another change required here, the above should be 'm' instead of 'cpumask'.

I am going to and make the suggested changes to this patch and will post it
with driver patches.
Please let me know if there are any objections to that.

>
> > +}
> > +
> >  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)
> >  {
> >
>
>
> --
> Thanks
> Nitesh



-- 
Thanks
Nitesh