[linux-audio-user] IRQ settings and low latency

Greg Jednaszewski greg at attenuated.org
Thu Mar 11 15:15:41 EST 2004


I've been working on getting my linux system set up for recording with
jack/ardour.  I came across the "Low Latency mini howto":

At the end, it talks about setting up IRQs such that the sound card is
at a high priority relative to other devices in the system.  However,
all the information in the doc pertains to non-APIC machines.  What
about an APIC-enabled machine?

The output of 'cat /proc/interrupts' shows my sound card (ICE1712) dead

           CPU0       CPU1       
  0:    6628091          0    IO-APIC-edge  timer
  1:          6          0    IO-APIC-edge  keyboard
  2:          0          0          XT-PIC  cascade
  9:          0          0          XT-PIC  acpi
 12:        803          0    IO-APIC-edge  PS/2 Mouse
 15:          5          0    IO-APIC-edge  ide1
 16:          0          0   IO-APIC-level  usb-uhci, usb-uhci
 18:       4178          0   IO-APIC-level  libata, usb-uhci
 19:        320          0   IO-APIC-level  usb-uhci
 20:       6406          0   IO-APIC-level  eth0
 21:          0          0   IO-APIC-level  ICE1712
NMI:          0          0 
LOC:    6628191    6628246 
ERR:          0
MIS:          0

output of: lspci -v -s 02:01.0   
02:01.0 Multimedia audio controller: IC Ensemble Inc ICE1712 [Envy24]
(rev 02)
        Subsystem: IC Ensemble Inc: Unknown device d634
        Flags: bus master, medium devsel, latency 32, IRQ 21
        I/O ports at 8000 [size=32]
        I/O ports at 8400 [size=16]
        I/O ports at 8800 [size=16]
        I/O ports at 8c00 [size=64]
        Capabilities: [80] Power Management version 1

I've tried manually setting IRQs in the BIOS, moving the card around,
etc.  No amount of tweaking can move it any higher in the list. (It's
set to IRQ 10 in the BIOS)

I guess my question is: Does the IRQ priority matter when IRQs are
abstracted by the APIC?  If so, how does one change the priority in this
situation?  I'm running 2.4.22, with the low latency and kernel
preemption patches installed.


Greg Jednaszewski
greg at attenuated.org

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