netdev - Re: [patchlet] r8169: fix napi_schedule_irqoff() called with irqs enabled warning

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Date:   Fri, 16 Oct 2020 16:41:50 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Mike Galbraith <efault@....de>, netdev <netdev@...r.kernel.org>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>
Subject: Re: [patchlet] r8169: fix napi_schedule_irqoff() called with irqs
 enabled warning

On 16.10.2020 16:26, Vladimir Oltean wrote:
> On Fri, Oct 16, 2020 at 01:34:55PM +0200, Heiner Kallweit wrote:
>> I'm aware of the topic, but missing the benefits of the irqoff version
>> unconditionally doesn't seem to be the best option.
> 
> What are the benefits of the irqoff version? As far as I see it, the
> only use case for that function is when the caller has _explicitly_
> disabled interrupts.
> 
If the irqoff version wouldn't have a benefit, then I think we wouldn't
have it ..

> The plain napi_schedule call will check if irqs are disabled. If they
> are, it won't do anything further in that area. There is no performance
> impact except for a check.
> 
There is no such check, and in general currently attempts are made to
remove usage of e.g. in_interrupt(). napi_schedule() has additional calls
to local_irq_save() and local_irq_restore().

>> Needed is a function that dynamically picks the right version.
> 
> So you want to replace a check with another check, am I right? How will
> that improve anything performance-wise?
>