linux-kernel - Re: [PATCH 2/5] genirq: Allow the affinity of a percpu interrupt to be set/retrieved

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Date:	Thu, 19 May 2016 15:25:16 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Jason Cooper <jason@...edaemon.net>,
	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/5] genirq: Allow the affinity of a percpu interrupt to
 be set/retrieved

Hi Marc,

On Thu, May 19, 2016 at 3:13 PM, Marc Zyngier <marc.zyngier@....com> wrote:
> On 19/05/16 12:08, Geert Uytterhoeven wrote:
>> On Mon, Apr 11, 2016 at 10:57 AM, Marc Zyngier <marc.zyngier@....com> wrote:
>>> In order to prepare the genirq layer for the concept of partitionned
>>> percpu interrupts, let's allow an affinity to be associated with
>>> such an interrupt. We introduce:
>>>
>>> - irq_set_percpu_devid_partition: flag an interrupt as a percpu-devid
>>>   interrupt, and associate it with an affinity
>>> - irq_get_percpu_devid_partition: allow the affinity of that interrupt
>>>   to be retrieved.
>>>
>>> This will allow a driver to discover which CPUs the per-cpu interrupt
>>> can actually fire on.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
>>
>>> --- a/include/linux/irqdesc.h
>>> +++ b/include/linux/irqdesc.h
>>> @@ -66,6 +66,7 @@ struct irq_desc {
>>>         int                     threads_handled_last;
>>>         raw_spinlock_t          lock;
>>>         struct cpumask          *percpu_enabled;
>>> +       const struct cpumask    *percpu_affinity;
>>
>> Adding this field showed up on my bloat-o-meter radar...
>
> By how much?

By NR_IRQS * 4 bytes, which ranges from 32 to 1024 bytes on m68k,
depending on the platform.

>> Does it make sense to move it (and percpu_enabled) inside the "#ifdef
>> CONFIG_SMP" below, and rework the code to not need it on UP?
>>
>>>  #ifdef CONFIG_SMP
>>>         const struct cpumask    *affinity_hint;
>>>         struct irq_affinity_notify *affinity_notify;
>
> I wonder if we couldn't actually unify affinity_hint and
> percpu_affinity. I'll have a look.

Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds