linux-kernel - Re: [PATCHv2 5/5] irqchip/GICv3: make reschedule-ipi light weight

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Date:   Wed, 29 Sep 2021 08:24:34 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Joey Gouly <joey.gouly@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Julien Thierry <julien.thierry@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yuichi Ito <ito-yuichi@...itsu.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 5/5] irqchip/GICv3: make reschedule-ipi light weight

On Fri, 24 Sep 2021 14:28:37 +0100,
Pingfan Liu <kernelfans@...il.com> wrote:
> 
> To achieve the light weight as
> DEFINE_IDTENTRY_SYSVEC_SIMPLE(sysvec_reschedule_ipi) on x86, it had
> better treat irqnr differently at the frontend. And let IPI_RESCHEDULE
> call __irq_enter_raw() instead of irq_enter_rcu().
> 
> Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Joey Gouly <joey.gouly@....com>
> Cc: Sami Tolvanen <samitolvanen@...gle.com>
> Cc: Julien Thierry <julien.thierry@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Yuichi Ito <ito-yuichi@...itsu.com>
> Cc: linux-kernel@...r.kernel.org
> To: linux-arm-kernel@...ts.infradead.org
> ---
>  drivers/irqchip/irq-gic-v3.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 906538fa8771..593d4539a209 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -709,6 +709,9 @@ static void gic_handle_nmi(struct pt_regs *regs)
>  		gic_deactivate_unhandled(irqnr);
>  }
>  
> +/* RESCHEDULE IPI hwirq nr is 0, and the only raw one */
> +static unsigned long raw_interrupt_mask = 1;

I'm afraid you have the wrong end of the stick. This isn't a GIC
property. This is an architecture decision, and only the architecture
can expose what they want.

	M.

-- 
Without deviation from the norm, progress is not possible.