Re: [PATCH 0/2] arm64: Allow the rescheduling IPI to bypass irq_enter/exit

Valentin Schneider
2020-11-10T15:49:12Z

On 01/01/70 01:00, Valentin Schneider wrote:
> On 10/11/20 13:03, Peter Zijlstra wrote:
>> On Mon, Nov 02, 2020 at 10:30:50AM +0000, Valentin Schneider wrote:
>>
>>> Now, I'd like to pen exactly why we think it's okay to forgo irq_{enter,
>>> exit}() for that one IRQ and not any other.
>>
>> Thomas already said a few words on this, but basically scheduler_ipi()
>> is a NOP (*almost*), the IPI has no body. All it does is tickle the
>> return-from-interrupt path. So any setup and tear-down done for the
>> non-existing body is a waste of time.

Gotcha.

The pedant in me thinks this makes it more of a handler property than an
IRQ one, but I don't see a nice way to e.g. have this as a flag passed to
__request_percpu_irq() and not have it usable by random modules.