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Date: Mon, 14 Jun 2021 12:12:38 -0400
From: Nitesh Lal <nilal@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Jesse Brandeburg <jesse.brandeburg@...el.com>,
Robin Murphy <robin.murphy@....com>,
Marcelo Tosatti <mtosatti@...hat.com>,
Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
intel-wired-lan@...ts.osuosl.org, jbrandeb@...nel.org,
"frederic@...nel.org" <frederic@...nel.org>,
"juri.lelli@...hat.com" <juri.lelli@...hat.com>,
Alex Belits <abelits@...vell.com>,
"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"rostedt@...dmis.org" <rostedt@...dmis.org>,
"peterz@...radead.org" <peterz@...radead.org>,
"davem@...emloft.net" <davem@...emloft.net>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
"stephen@...workplumber.org" <stephen@...workplumber.org>,
"rppt@...ux.vnet.ibm.com" <rppt@...ux.vnet.ibm.com>,
"jinyuqi@...wei.com" <jinyuqi@...wei.com>,
"zhangshaokun@...ilicon.com" <zhangshaokun@...ilicon.com>,
netdev@...r.kernel.org, chris.friesen@...driver.com,
Marc Zyngier <maz@...nel.org>,
Neil Horman <nhorman@...driver.com>, pjwaskiewicz@...il.com
Subject: Re: [PATCH] genirq: Provide new interfaces for affinity hints
On Mon, Jun 7, 2021 at 1:00 PM Nitesh Lal <nilal@...hat.com> wrote:
>
> On Fri, May 21, 2021 at 8:03 AM Thomas Gleixner <tglx@...utronix.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@...utronix.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
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