Re: [PATCH 2/2] arm64: smp: Don't directly call arch_smp_send_reschedule() for wakeup

Mark Rutland
2023-10-02T17:26:26Z

On Mon, Oct 02, 2023 at 09:45:30AM -0700, Douglas Anderson wrote:
> In commit 2b2d0a7a96ab ("arm64: smp: Remove dedicated wakeup IPI") we
> started using a scheduler IPI to avoid a dedicated reschedule. When we
> did this, we used arch_smp_send_reschedule() directly rather than
> calling smp_send_reschedule(). The only difference is that calling
> arch_smp_send_reschedule() directly avoids tracing. Presumably we
> _don't_ want to avoid tracing here, so switch to
> smp_send_reschedule().
>
> Fixes: 2b2d0a7a96ab ("arm64: smp: Remove dedicated wakeup IPI")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> I don't 100% know if this is correct and I don't have any hardware
> that uses the "ACPI parking protocol", but I think it's right. My main
> incentive for this is that it makes it easier to backport pseudo-NMI
> to kernels that don't have arch_smp_send_reschedule(), but I think
> it's also more correct.
>
> If for some reason we truly did want to avoid tracing here, please
> shout and we can drop this patch.

This should be sound, and I don't have strong feelings either way on this, so
FWIW:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

>
> arch/arm64/kernel/smp.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 0a6002243a8c..b530d8ef9c1d 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -1063,7 +1063,7 @@ void arch_send_wakeup_ipi(unsigned int cpu)
> * We use a scheduler IPI to wake the CPU as this avoids the need for a
> * dedicated IPI and we can safely handle spurious scheduler IPIs.
> */
> - arch_smp_send_reschedule(cpu);
> + smp_send_reschedule(cpu);
> }
> #endif
>
> --
> 2.42.0.582.g8ccd20d70d-goog