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Xen DOM0 pirq panic with lots of cores



I recently received a "new" system (anno 2017) for use with Xen; it has
two Xeon Scalable Gold 6138 CPUs with 20 cores each and 40 threads,
making a grand total of 80 CPUs seen by Xen and NetBSD.

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."

But this does not seem to be true in my case; booting a regular GENERIC
is perfectly fine while under Xen (with a XEN3_DOM0 from netbsd-11 daily
of this month) I run in to this panic:

[   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.

Staffan

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