netdev - Re: [PATCH net-next 1/2] net: add a napi variant for RT-well-behaved drivers

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Message-ID: <87pmxs1g4x.ffs@nanos.tec.linutronix.de>
Date:   Sat, 15 May 2021 11:49:02 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        simon.horman@...ronome.com, oss-drivers@...ronome.com,
        bigeasy@...utronix.de, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next 1/2] net: add a napi variant for RT-well-behaved drivers

On Fri, May 14 2021 at 15:24, Jakub Kicinski wrote:
>  /**
> - *	napi_schedule_irqoff - schedule NAPI poll
> - *	@n: NAPI context
> + * napi_schedule_irq() - schedule NAPI poll from hardware IRQ
> + * @n: NAPI context
>   *
>   * Variant of napi_schedule(), assuming hard irqs are masked.
> + * Hardware interrupt handler must be marked with IRQF_NO_THREAD
> + * to safely invoke this function on CONFIG_RT=y kernels (unless
> + * it manually masks the interrupts already).
>   */
> -static inline void napi_schedule_irqoff(struct napi_struct *n)
> +static inline void napi_schedule_irq(struct napi_struct *n)
>  {
>  	if (napi_schedule_prep(n))
> -		__napi_schedule_irqoff(n);
> +		__napi_schedule_irq(n);

As this is intended for the trivial

   irqhandler()
        napi_schedule_irq(n);
        return IRQ_HANDLED;

case, wouldn't it make sense to bring napi_schedule_irq() out of line
and have the prep invocation right there?

void napi_schedule_irq(struct napi_struct *n)
{
 	if (napi_schedule_prep(n))
		____napi_schedule(this_cpu_ptr(&softnet_data), n);
}
EXPORT_SYMBOL(napi_schedule_irq);

As that spares a function call and lets the compiler be smarter about
it. I might be missing something though, but at least brain is more
awake now :)

Thanks,

        tglx