[linux-audio-user] Tracking down overruns

[Benji Flaming]

> Welcome! I'm a Pro Tools user under Windows. On the Windows side we have
> not had these warnings about reducing disk cache, as far as I can
> remember...

I'm glad to meet you.  I've been playing with Pro Tools since 4.3.1, and my
studio is running currently running MIX plus on an old beige G3/300 running
MacOS 9.  I've often wanted to migrate over to Windows, but we'd lose all of
our plug-ins.  Pro Tools is actually one of my biggest motives for moving to
Linux - one gets tired of jumping through flaming hoops every time
DigiDesign or Apple release new hardware or software.

> Forgiven. No problem. However, this means you are doing latency testing
> to your system drive. Is this correct? You do not have a second,
> separate audio drive at this point? I ask as I notice you have the
> Promise ATA controller on IRQ11.

Well...I *do* have a third drive hooked up to the Promise controller, but
upon installing it, I discovered that my power supply doesn't want to supply
power to another drive - even though I have enough power hookups.  I can
only use the drive if I disconnect power from my LS120, CD-ROM or Windows
hard drive.  Time to buy a new power supply....

> Also, maybe I forgot, but what windowing environment are you running?
> KDE? Gnome? I run fluxbox and think it's quite nice for audio, if you
> like minimalistic environments. I raise this question as I had a lot fo
> similar problems with KDE, and never tried Gnome after I got fluxbox
> working well. (And it's very easy to try out without effecting what ever
> your other environment is.)

I'm running Blackbox - we seem to be cousins.

For what it's worth, I've also posted my XF86Config:
http://www.comevisit.com/NorthernSunrise/latency/XF86Config
It has a few things I need to fix, but nothing that I think would affect
audio performance.

> OK, one potential problem I spot is the IRQ for your audio controller is
> about the worst it could have at IRQ5. As a Mac guy you are forgiven if
> you don't realize how screwed up Intel architecture interrupts are. The

My machine is absolutely adamant that the sound card *has* to go there :(  I
spent many frustrating and fruitless hours trying to address this issue.  I
sifted through every single BIOS setting, juggled the cards all over the
place, but the only way I could get the card off IRQ 5 was by disabling that
IRQ.  When I did this, it moved the card up to IRQ 4, and so on.  In short,
my machine *always* gives the sound card the lowest-priority IRQ, and
provides no way (that I could find) to assign IRQs manually.  Ultimately, I
put things back as they were, and decided to be more careful next time I buy
a board.

I *might* be able to force it to share an IRQ with something else.  Would
this be worth tampering with?

> (Strange that the Promise is there in lspci but doesn't show up in
> /proc/interrupts. Maybe some more knowledgeable Linux person could help
> me understand why. I don't know...

Since I wasn't ready to use it, I don't think I built drivers for it when I
built the kernel.  Might this explain the discrepancy?

Also, I've done quite a bit of scouring around for information on disk cache
settings.  Mostly, what I find are messages asking how to set a maximum disk
cache size, followed by silence, or by replies saying not to bother with it.
Often the discussion quickly descends into a debate about the soundness of
Linux's VM system, with the original question about the disk cache system
being ignored.  I did find a patch by Rik van Riel
(http://surriel.com/patches/2.4/2.4.20-rmap15c) which appears to provide
sysctl parameters for cache size restraints, but I'd have to download and
build a 2.4.20 kernel, downgrade my module utilities, etc.

Even if something else is causing my overruns now, I certainly suspect that
real-time performance could be enhanced by a bit of cache settings tweaking.
If anyone has any info on doing this with a 2.6.test5 kernel, I would love
to get it.  My curiosity has been awakened :)

Thanks again for the continued help!

|)
|)enji

Benjamin Flaming
--------------------
"The trouble with computers, of course, is that they're very sophisticated
idiots."