Re: [PATCH 3/4] arm64: wire SDEI NMI into the hardlockup watchdog

[Doug Anderson]

Hi,

On Wed, Jun 3, 2026 at 7:36 AM Kiryl Shutsemau <kirill@xxxxxxxxxxxxx> wrote:
>
> From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>
>
> Select HAVE_HARDLOCKUP_DETECTOR_ARCH so the framework takes its backend
> from this driver. A per-CPU hrtimer checks its buddy's heartbeat and
> signals event 0 at a stalled CPU, which runs watchdog_hardlockup_check()
> NMI-like.
>
> The source is chosen at boot: SDEI if firmware provides it, otherwise a
> perf-NMI counter (pseudo-NMI) fallback -- one image covers both.
>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> ---
>  arch/arm64/Kconfig          |   1 +
>  drivers/firmware/Kconfig    |   3 +
>  drivers/firmware/sdei_nmi.c | 247 +++++++++++++++++++++++++++++++++++-
>  3 files changed, 248 insertions(+), 3 deletions(-)

I'm a little confused about this patch. We already have a buddy
hardlockup detector using the hrtimer, and it's even been improved
recently to trigger in a smaller time bound. It looks as if you're
duplicating bits of the perf and buddy detector here?

I don't think you need this patch at all. The existing buddy detector
+ patches #1 and #2 in your series should be sufficient.

Did I misunderstand?

-Doug