linux-kernel - Re: [PATCH v3 1/3] irqchip/loongson-eiointc: Skip handling if there is no pending irq

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Date: Wed, 24 Jan 2024 17:51:23 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Jiaxun Yang <jiaxun.yang@...goat.com>, Thomas Gleixner <tglx@...utronix.de>, 
	linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Sergey Shtylyov <s.shtylyov@....ru>, lvjianmin@...ngson.cn
Subject: Re: [PATCH v3 1/3] irqchip/loongson-eiointc: Skip handling if there
 is no pending irq

Hi, Bibo,

On Thu, Jan 18, 2024 at 8:15 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> There is one simple optimization in the interrupt dispatch function
> eiointc_irq_dispatch. There are 256 IRQs supported for eiointc, eiointc
> irq handler reads the bitmap and find pending irqs when irq happens.
> So there are four times of consecutive iocsr_read64 operations for the
> total 256 bits to find all pending irqs. If the pending bitmap is zero,
> it means that there is no pending irq for the this irq bitmap range,
> we can skip handling to avoid some useless operations such as clearing
> hw ISR.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>  drivers/irqchip/irq-loongson-eiointc.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/irqchip/irq-loongson-eiointc.c b/drivers/irqchip/irq-loongson-eiointc.c
> index 1623cd779175..6143adb1b73b 100644
> --- a/drivers/irqchip/irq-loongson-eiointc.c
> +++ b/drivers/irqchip/irq-loongson-eiointc.c
> @@ -198,6 +198,17 @@ static void eiointc_irq_dispatch(struct irq_desc *desc)
>
>         for (i = 0; i < eiointc_priv[0]->vec_count / VEC_COUNT_PER_REG; i++) {
>                 pending = iocsr_read64(EIOINTC_REG_ISR + (i << 3));
> +
> +               /*
> +                * Get pending eiointc irq from bitmap status, there are 4 times
> +                * consecutive iocsr_read64 operations for 256 IRQs.
> +                *
> +                * Skip handling if pending bitmap is zero
This driver is shared by Loongson-2 and Loongson-3 series, for
Loongson-2K0500 there is only 128 IRQs, so I suggest only keep the
last line "Skip handling if current pending bitmap is zero" is enough.

Huacai

> +                */
> +               if (!pending)
> +                       continue;
> +
> +               /* Clear the IRQs */
>                 iocsr_write64(pending, EIOINTC_REG_ISR + (i << 3));
>                 while (pending) {
>                         int bit = __ffs(pending);
> --
> 2.39.3
>