Re: [LAU] IRQ tuning

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On Sat, Jun 02, 2007 at 12:00:30PM +0200, Roman Mu??oz wrote:
> Hi,
>
> After some days browsing for info, it looks like I'm being unable to
> tune my IRQs to get my sound card on its own, exclusive IRQ.
>
> I'm using 2.6.21.3-rt9 on Debian Etch now, but:
>
> a) sound card is on IRQ 17 with ehci on IRQ 17 too. Both sound card
> (intel hda) and usb are motherboard (NVIDIA CK 804) ones. I'm not
> getting xruns, and I was thinking it was quite fine and probably
> hardware-related.
>
> b) However, I can not get those nice 255 IRQ vectors even if local apic
> and io-apic on uniprocessor are active. I even tried to use debian
> kernel configuration as much as possible (on 2.6.18 I get the vectors)
> but they seem to be unavailable as soon as I patch the kernel with
> Ingo's patch.
>
> So I think now this could be software-related and I would be able to set
> IRQs. What's the matter? Could you guys give me some up-to-date pointers?
>

I went through this wringer, it took 6 months, and I've posted here and on the jack-dev and freebob lists, about it, and blogged about it extensively too. Hopefully my experience will save you time, money, and headaches.

The conclusions I came to are:

1) If you are on a machine with PCI slots, you can change your IRQ mappings by physically moving your cards into different slots. Trial and error is the only thing that works here.

2) If you have a laptop, or otherwise have to use the built-in chips on the motherboard, you are stuck with whatever IRQ mapping you've got, unless your BIOS offers you the option to change them. The only BIOS I have heard of which allows this, is IBM/Lenovo's on their ThinkPad's.

3) The hda-intel chip is complete and utter crap, and is unsuited for any serious RT audio use. Get a USB or firewire interface. Then again, if all you're doing is playing music from softsynths (not recording live audio), in stereo and not 5-channel surround, and it works for you, then you can probably continue using the hda-intel without worrying about it.

4) If you decide to go with firewire, make sure you don't have a Ricoh chip (lspci will tell you). They have a bug in their streaming implementation and simply do not work for audio. The TI chips work well, and are specifically recommended by some firewire audio manufacturers (i.e. Edirol).

5) Use Debian Sid (not Etch), or Sidux, or even easier, a music distro like UbuntuStudio, 64Studio, Musix, etc, which are Debian-based anyway.

6) If you're using softsynths, or LADSPA plugins and other DSP stuff, get the absolutely fastest CPU(s) that you can (or can't) afford.

Anyway, YMMV, etc, but the above worked for me and I'm happy with the results.

- -ken
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Received on Mon Jun 4 08:15:01 2007