Re: [PATCH v11 3/6] arm64: smp: Remove dedicated wakeup IPI

[Stephen Boyd]

Quoting Douglas Anderson (2023-08-24 08:30:29)
> From: Mark Rutland <mark.rutland@xxxxxxx>
>
> To enable NMI backtrace and KGDB's NMI cpu roundup, we need to free up
> at least one dedicated IPI.
>
> On arm64 the IPI_WAKEUP IPI is only used for the ACPI parking protocol,
> which itself is only used on some very early ARMv8 systems which
> couldn't implement PSCI.
>
> Remove the IPI_WAKEUP IPI, and rely on the IPI_RESCHEDULE IPI to wake
> CPUs from the parked state. This will cause a tiny amonut of redundant
> work to check the thread flags, but this is miniscule in relation to the
> cost of taking and handling the IPI in the first place. We can safely
> handle redundant IPI_RESCHEDULE IPIs, so there should be no functional
> impact as a result of this change.
>
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Sumit Garg <sumit.garg@xxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> ---

Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>