Subject: Re: [linux-audio-user] Is everyone sick of interrupts yet?
From: Russell Hanaghan (hanaghan_AT_starband.net)
Date: Wed Sep 29 2004 - 10:07:18 EEST
On Tuesday 28 September 2004 09:57 am, Mark Knecht wrote:
> Mark Knecht wrote:
> > brad stafford wrote:
> >> I just tonight switched from the Planet CCRMA RH9 to FC1. The install
> >> was purely from the CDROMs dated 4/25/2004.
> >>
> >> I've seen all the latest posts about interrupts and did the required
> >> reading on the internet. I really managed to get RH9 cleaned up but in
> >> FC1 I'm seeing something a little different. I have a Delta 1010 and I'm
> >> running an AMD Barton 2.6 with 5 PCI slots. The question is what the
> >> heck are IRQ 16 and 22? I moved the sound and ethernet cards around to
> >> get them to 16 and 22 as they used to be eth0 on 21 and ICE1712 on 22. I
> >> have ACPI turned off as a service but don't have a "disable" option in
> >> the BIOS. I did turn off USB support in the BIOS.
> >>
> >> Is 16 like the equivalent of IRQ 3 since it's following 15?
> >>
> >> [brad_AT_mars brad]$ cat /proc/interrupts
> >> CPU0
> >> 0: 81690 IO-APIC-edge timer
> >> 1: 75 IO-APIC-edge keyboard
> >> 2: 0 XT-PIC cascade
> >> 8: 1 IO-APIC-edge rtc
> >> 9: 0 IO-APIC-level acpi
> >> 12: 836 IO-APIC-edge PS/2 Mouse
> >> 14: 10789 IO-APIC-edge ide0
> >> 15: 735 IO-APIC-edge ide1
> >> 16: 0 IO-APIC-level ICE1712
> >> 22: 21 IO-APIC-level eth0
> >> NMI: 0
> >> LOC: 81633
> >> ERR: 0
> >> MIS: 0
> >>
> >> I'm getting 5.8 msec latency in JACK with 128 frames/period at 44100 and
> >> 2 periods/buffer. A huge improvement over the 46.1 msec using RH9 with
> >> capabilities.
> >>
> >> Thanks, Brad.
> >
> > Brad,
> > First I see no reason for you to change anything. If there's no
> > problem to fix, then why make a problem?
> >
> > Interrupts, in your case, are based on the APIC model. You machine
> > has an APIC (Advanced Programmable Interrupt Controller) as well as one
> > or more IO-APIC chips, so it supports more than the old style 15
> > interrupts. This is not a problem. It should be an advantage, if
> > everything is set up correctly.
> >
> > My input would be to go with the flow. If one of these days you find
> > that you are getting worse performance, be it xruns or something else,
> > then come back and let's look at the setup of the machine. Until then,
> > be happy. It looks like the results are quite good, right?!?
> >
> > Cheers,
> > Mark
>
> One last little sickening detail I forgot to add before. Sorry for doing
> it now.
>
> In the older 'compatibility model' we knew the 'prioity of the interrupt
> from the interrupt number: 0,1,8,9,10,11,12,13,14,15,3,4,5,6,7. It was
> hardwired.
>
> In the newer 'APIC' model all we know is the interrupt number, not the
> priority. There is a secondary routing table that maps the interrupt
> priority using a vector. The table is visible in dmesg on my machines.
> It probably is on yours also. The meaning of the table is obscure and
> has been covered here before. The 'unfortunate' aspect of the table is
> that there are no generally avaialble tools to allow a system
> administrator to modify the vectors and hence change the priorities of a
> given hardware device. Not sure that matters to most people. I would be
> happier having that capability and hope it will appear one day.
>
> Sorry for chiming in again.
>
> - Mark
Aieeee! And we almost got away clean too! :)
R~
-- The Road of Life is paved with Squirrels that couldn't make a decision!
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