I have this note in my rtirq configuration file, it may be useful,
especially the reference to the web page at the end with discussion by
rtirq author:
# Note found on
rnbc.org:
# take note that rtirq:
# a. only honors one and only one driver thread per IRQ line,
# so if IRQ share the same line only one can be prioritized
# b. the "snd" particle applies to PCI audio devices;
# "usb" is generic for (all) USB host controllers and applies
# for all USB devices including audio ones; if you want
# specific ports only to get prioritized, then use the respective
# trait (eg. "usb1", "usb2", etc. you'll have to dig which one
# exactly is right, coz it depends on which physical USB host port
# is the device plugged in).
# see
http://www.rncbc.org/drupal/node/850
--
Chris Caudle