FWIW, these messages:
Uhhuh. NMI received for unknown reason 31 on CPU 0.
Do you have a strange power saving mode enabled?
Dazed and confused, but trying to continue
occur whether booted to 13.1, 13.2, 42.1, TW, Fedora, Mageia or Jessie. They
are most reliably triggered by opening an HTML5 Youtube video. Neither nohpet
nor nmi_watchdog=0 nor BIOS changes have any perceptible effect on their
occurrence.