Maybe the timer interrupt has a sufficiently high priority and latency is
low? Maybe cia_set_irq() is really expensive?
I don't know the platform well enough so I'm inclined to revert. We can
benchmark gettimeofday syscalls on elgar but is that hardware
representative of other relevant models?
[1]
https://github.com/mamedev/mame/commit/e2ed0490520f538c346c8bdaa9084bcbc43427cb
[2]
http://vice-emu.sourceforge.net/vice_9.html
[3]
https://www.commodore.ca/manuals/funet/cbm/documents/chipdata/cia6526.zip