Re: [PATCH v6 20/29] init/main: Delay initialization of the lockup detector after smp_init()

[Ricardo Neri <ricardo.neri-calderon@linux.intel.com>]

On Tue, May 10, 2022 at 08:38:22PM +1000, Nicholas Piggin wrote:
> Excerpts from Ricardo Neri's message of May 6, 2022 9:59 am:
> > Certain implementations of the hardlockup detector require support for
> > Inter-Processor Interrupt shorthands. On x86, support for these can only
> > be determined after all the possible CPUs have booted once (in
> > smp_init()). Other architectures may not need such check.
> > 
> > lockup_detector_init() only performs the initializations of data
> > structures of the lockup detector. Hence, there are no dependencies on
> > smp_init().
> 

Thank you for your feedback Nicholas!

> I think this is the only real thing which affects other watchdog types?

Also patches 18 and 19 that decouple the NMI watchdog functionality from
perf.

> 
> Not sure if it's a big problem, the secondary CPUs coming up won't
> have their watchdog active until quite late, and the primary could
> implement its own timeout in __cpu_up for secondary coming up, and
> IPI it to get traces if necessary which is probably more robust.

Indeed that could work. Another alternative I have been pondering is to boot
the system with the perf-based NMI watchdog enabled. Once all CPUs are up
and running, switch to the HPET-based NMI watchdog and free the PMU counters.

> 
> Acked-by: Nicholas Piggin <npiggin@gmail.com>

Thank you!

BR,
Ricardo