netdev - Re: [PATCH v5 01/14] genirq: Provide new interfaces for affinity hints

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Message-ID: <CAFj5m9+9asdQOCRHb0tZ=XSD-sOj+RLEDVEAObN81Z9y1JcgQg@mail.gmail.com>
Date:   Fri, 6 Aug 2021 23:51:58 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Nitesh Narayan Lal <nitesh@...hat.com>
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Subject: Re: [PATCH v5 01/14] genirq: Provide new interfaces for affinity hints

On Wed, Jul 21, 2021 at 7:26 AM 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

Reviewed-by: Ming Lei <ming.lei@...hat.com>