i/o is very slow on FreeBSD dom0 with Xen-4.12 and Freebsd-12

[Roger Pau Monné]

On Tue, Oct 15, 2019 at 08:56:22AM -0700, Brian Buhrow wrote:
> 	hello Roger.  Sorry, my bad.  I didn't even look at the cause of the
> panic.   Rebooting the system caused it to come up clean after another pass
> with fsck.  With the ioapic_ack=old argument, the system comes up right
> away and is quite responsive.
> 	Can you explain how to select which argument to use on the command
> line if the autoselection code doesn't work?

Hm, it's not so much that the autodetection is wrong, AFAIK there's
some hardware issue with specific models that make the new ack method
not work properly. This is limited to very specific (and older)
models. Note that you might still see interrupt timeouts with the old
ack method.

I will try to figure out if there's any hardware errata that could be
related to this issue, and try to find a box to reproduce (this might
not be feasible since I'm not sure I have anything similar to your
hardware available).

Roger.