Re: [PATCH v5 0/4] arm64: cross-CPU NMI via SDEI

Hi,

On Tue, Jul 28, 2026 at 5:18=E2=80=AFAM Kiryl Shutsemau <[email protected]> wr=
ote:
>
> The piece that isn't boot-time yet is the hardlockup detector that drives
> all this. perf and buddy are mutually exclusive at compile time. We want
> to use perf watchdog for FEAT_NMI while SDEI needs buddy.

FWIW: can I ask why? You're worried about the "all CPUs lock up at the
same time" problem? I am aware of some work towards solving that (even
with buddy) by letting the hardware watchdog driver's "bark" interrupt
run at NMI-level (or pseudo-NMI-level). With that change, I'm not
aware of any benefits of the "perf" detector over the buddy one. The
buddy one should generally be more efficient (fewer interrupts to
process) and less resource intensive (doesn't reserve a perf counter
for the whole boot).


> But it is solvable.

Yeah, someone posted proof-of-concept patches that made both
selectable at boot time. Nobody was really interested in shepherding
those patches all the way through.

-Doug