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Date: Fri, 25 Jun 2021 13:52:04 -0400
From: Nitesh Lal <nilal@...hat.com>
To: linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
linux-scsi@...r.kernel.org
Cc: intel-wired-lan@...ts.osuosl.org,
Thomas Gleixner <tglx@...utronix.de>, netdev@...r.kernel.org,
linux-pci@...r.kernel.org,
Jesse Brandeburg <jesse.brandeburg@...el.com>,
Robin Murphy <robin.murphy@....com>,
Marcelo Tosatti <mtosatti@...hat.com>,
Ingo Molnar <mingo@...nel.org>, jbrandeb@...nel.org,
frederic@...nel.org, Juri Lelli <juri.lelli@...hat.com>,
Alex Belits <abelits@...vell.com>,
Bjorn Helgaas <bhelgaas@...gle.com>, rostedt@...dmis.org,
peterz@...radead.org, davem@...emloft.net,
akpm@...ux-foundation.org, sfr@...b.auug.org.au,
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Stefan Assmann <sassmann@...hat.com>,
Tomas Henzl <thenzl@...hat.com>, kashyap.desai@...adcom.com,
Sumit Saxena <sumit.saxena@...adcom.com>,
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Subject: Re: [PATCH v1 01/14] genirq: Provide new interfaces for affinity hints
On Thu, Jun 17, 2021 at 2:23 PM Nitesh Narayan Lal <nitesh@...hat.com> wrote:
>
> From: Thomas Gleixner <tglx@...utronix.de>
>
> 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@...utronix.de>
> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
> Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@intel.com
> ---
> 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
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