The config of the Ubuntu Studio Precise kernel 3.2.0-23-lowlatency, seems to be ready to use it with threadirqs as boot option.
Anyway, I still get
$ /etc/init.d/rtirq status
PID CLS RTPRIO NI PRI %CPU STAT COMMAND
92 FF 90 - 130 0.0 S irq/8-rtc0
85 FF 85 - 125 0.0 S irq/18-ohci_hcd
89 FF 84 - 124 0.0 S irq/18-ohci_hcd
611 FF 83 - 123 0.0 S irq/18-snd_hdsp
1285 FF 82 - 122 0.8 S irq/18-nvidia
652 FF 80 - 120 0.0 S irq/20-snd_ice1
656 FF 80 - 120 0.0 S irq/21-snd_ice1
instead the of the wanted
$ /etc/init.d/rtirq status
PID CLS RTPRIO NI PRI %CPU STAT COMMAND
384 FF 90 - 130 0.0 S irq/8-rtc0
1102 FF 85 - 125 0.0 S irq/18-hdspm
1123 FF 80 - 120 0.0 S irq/20-ICE1712
1135 FF 80 - 120 0.0 S irq/21-ICE1712
So for the moment I guess it's better instead of using
$ grep RTIRQ_NAME_LIST /etc/default/rtirq
RTIRQ_NAME_LIST="rtc hdspm snd usb i8042"
which does the trick for other installs, to use
$ grep RTIRQ_NAME_LIST /etc/default/rtirq
RTIRQ_NAME_LIST="rtc snd usb i8042"
since this results in
$ /etc/init.d/rtirq status
PID CLS RTPRIO NI PRI %CPU STAT COMMAND
92 FF 90 - 130 0.0 S irq/8-rtc0
702 FF 85 - 125 0.0 S irq/20-snd_ice1
724 FF 85 - 125 0.0 S irq/21-snd_ice1
717 FF 83 - 123 0.0 S irq/18-snd_hdsp
1348 FF 82 - 122 0.8 S irq/18-nvidia
78 FF 80 - 120 0.0 S irq/19-ehci_hcd
80 FF 80 - 120 0.3 S irq/16-ohci_hcd
82 FF 79 - 119 0.0 S irq/17-ohci_hcd
84 FF 78 - 118 0.0 S irq/18-ohci_hcd
87 FF 78 - 118 0.0 S irq/17-ohci_hcd
89 FF 77 - 117 0.0 S irq/18-ohci_hcd
91 FF 75 - 115 0.0 S irq/1-i8042
20 FF 50 - 90 0.0 S irq/9-acpi
67 FF 50 - 90 0.2 S irq/22-ahci
279 FF 50 - 90 0.0 S irq/14-pata_ati
280 FF 50 - 90 0.0 S irq/15-pata_ati
292 FF 50 - 90 0.0 S irq/22-firewire
561 FF 50 - 90 0.0 S irq/7-parport0
1020 FF 50 - 90 0.0 S irq/43-eth0
3 TS - 0 19 0.2 S ksoftirqd/0
9 TS - 0 19 0.2 S ksoftirqd/1
so my MIDI interfaces snd_ice1... get a higher priority than the audio card snd_hdsp..., but at least all the other stuff get a lower priority.
On other installs I also got/get the wanted priority for a non-rt, with threadirqs, e.g.:
spinymouse@avlinux:~$ uname -a
Linux avlinux 3.0.23-avl-7-pae #28 SMP PREEMPT Thu Mar 1 19:14:14 EST 2012 i686 GNU/Linux
spinymouse@avlinux:~$ /etc/init.d/rtirq status
PID CLS RTPRIO NI PRI %CPU STAT COMMAND
452 FF 90 - 130 0.0 S irq/8-rtc0
1028 FF 85 - 125 0.0 S irq/18-hdspm
1040 FF 80 - 120 0.0 S irq/20-ICE1712
1042 FF 80 - 120 0.0 S irq/21-ICE1712
615 FF 75 - 115 0.0 S irq/19-ehci_hcd
620 FF 75 - 115 0.2 S irq/16-ohci_hcd
622 FF 74 - 114 0.0 S irq/17-ohci_hcd
626 FF 73 - 113 0.0 S irq/17-ohci_hcd
445 FF 70 - 110 0.0 S irq/1-i8042
96 FF 50 - 90 0.0 S irq/9-acpi
621 FF 50 - 90 0.1 S irq/22-firewire
625 FF 50 - 90 0.0 S irq/18-ohci_hcd
627 FF 50 - 90 0.0 S irq/18-ohci_hcd
628 FF 50 - 90 0.0 S irq/14-pata_ati
629 FF 50 - 90 0.0 S irq/15-pata_ati
634 FF 50 - 90 0.3 S irq/22-ahci
909 FF 50 - 90 0.0 S irq/7-parport0
1414 FF 50 - 90 0.0 S irq/43-eth0
3 TS - 0 19 0.0 S ksoftirqd/0
9 TS - 0 19 0.0 S ksoftirqd/1
Could it be the kernel version or video driver?
Any hints are welcome,
Ralf
PS: I did not test if it really does matter if the audio card has a higher or lower priority than the MIDI cards.