[linux-audio-user] APIC is bad?

Mark Knecht mknecht at controlnet.com
Fri Jul 16 11:19:48 EDT 2004

R Parker wrote:
> --- Mark Knecht <mknecht at controlnet.com> wrote:
>>Personally I have done no optimization work on APIC
>>systems and cannot 
>>tell you what would be best. However, TTBOMK, there
>>is no simple way 
>>today to optimize APIC interrupts in a Linux system
>>anyway, so as far as 
>>I can tell you basically take what you get. If you
>>get too many xruns 
>>then I guess you go back to non-APIC mode.
> My recolector is awful faulty but I seem to recall
> Clemens Ladisch having written something for APIC
> interupt ordering. Is my condition even worse than I'm
> aware of?
> ron
No, you are exactly right. Clemens and I have some small technical 
disagreements on this subject. We had a conversation that was 
interesting but I think didn't yield any clear answers, at least in my 
mind, so I freely admit I'm still confused on the subject.

I design PC hardware for a living and have worked on chipsets while at 
AMD. I understand the older style interrupt controller structure very 
well. APIC stuff came along after I left to work on 1394 stuff so I 
don't know it as well. As I remember the conversation the interrupt 
order was from the highest interrupt number and going down from there, 
so if Florin sees 25 interrupts, then #25 gets serviced first and that 
would be where I'd want my sound card, if I could get it there. (How you 
do this is not clear...)

If I remember Clemens POV on this subject he said it didn't matter what 
APIC IRQ you choose. I somehow felt that choosign a bad one had to cause 
stuff like xrun problems, but I haven't tried to test this hypothesis.


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