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

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Subject: Re: [linux-audio-user] IRQ settings and low latency
From: cv223_AT_comcast.net
Date: Fri Mar 12 2004 - 19:42:01 EET

I have the exact same problem and the exact same questions. I haven't seen any responses to Greg's email, so I thought I would reiterate the question. Anyone have any insight?

Thanks,

Joel
> Hi,
>
> I've been working on getting my linux system set up for recording with
> jack/ardour. I came across the "Low Latency mini howto":
> http://www.djcj.org/LAU/guide/Low_latency-Mini-HOWTO.php3
>
> 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
> last:
>
> 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.
>
> Thanks,
> Greg
>
> --
> Greg Jednaszewski
> greg_AT_attenuated.org

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