OK, that explains the kernel panics. Thanks for the info, that solved it!
FWIW, none of the IRIX CDs I have are in ISO format:
file 812-0505-001.img 812-0505-001.img: SGI disk label (volume header)
I dumped them using Linux 'dd' from the original CDs.
When I run with these CD images, even with the '-cdrom' command I get a SEGV because it looks like MAME is expecting them to be ISO. Hmm. I'll have to try the actual CD in a PC and see if it can mount it. Maybe there's a hybrid format or something else going on here. Linux treats them as EFS.
As far as performance goes, I wasn't complaining. I just wanted to know what to expect.
Thanks again for all the hard work that went into this! It's great to see this old stuff running again.