Re: Xen DOM0 pirq panic with lots of cores

[Greg Troxel <gdt%lexort.com@localhost>]

Staffan Thomen <staffan%shangtai.net@localhost> writes:

> The Xen howto wiki page states that dom0_max_vcpus and dom0_vcpus_pin
> is no longer necessary;
>
> "With NetBSD 10 and up, there does not seem to be an argument that
> pinning or limiting CPUs is a good idea."

I probably wrote that, and if so it was meant in terms of the intended
purposes not being useful, and it did not mean that I was sure there
were no bugs that would be avoided.  Don't take it too seriously.

> [   1.0000030] panic: pirq 16639 out of bound, increase  NR_PIRQS
>
> Limiting the CPUs to 1 like I used to avoid this issue an everything
> works like I'd expect.
>
> It seems like some discrepancy between GENERIC vs. XEN3_DOM0 here?
>
> The system is not yet in production so I can do tests for a brief time
> if necessary.

I (who is unlikely to fix this) would be interested in

  what is the highest number of cpus that is stable?  even roughly from
  binary search, might be interesting.

  what is the value of NR_PIRQS in GENERIC and XEN3_DOM0?   Is this as
  simple as a default being different?

  If this panic can happen, why are CPUs that would put things over the
  limit alllowed to attach?   (a hard question to answer probably)