Re: [gentoo-user] bad jack(?) performance

[Mark Knecht]

On 10/12/05, Matt Garman <garman@××××××××××.net> wrote:
> On Wed, Oct 12, 2005 at 06:48:48PM -0700, Mark Knecht wrote:
> > ...alsaplayer requires that you say you want to use realtime
> > capabilities:
> > alsaplayer -r -o jack
> > ...
> > Yeah, just the -r most likely. Also, depending on your sound card
> > 128/2 might be a bit tight, but let's try for it and see what happens.
>
> Unfortunately, adding the -r had no effect as far as I can tell.
>
> According to the alsaplayer manpage,
>
>           -r, --realtime
>           Enable realtime scheduling.  To  use  this  as a  normal
>           user,  alsaplayer must be SUID root.
>
> So I tried setting alsaplayer SUID root:
>
> # chmod u+s `which alsaplayer`
>
> Then as a regular (non-root) user:
>
> # alsaplayer -r -o jack &
> Gtk-WARNING **: This process is currently running setuid or setgid.
> This is not a supported use of GTK+. You must create a helper
> program instead. For further details, see:
>
>     http://www.gtk.org/setuid.html
>
> Refusing to initialize GTK+.
> [2]  + exit 1     alsaplayer -r -o jack
>
> I'm guessing that most folks don't have to worry about the whole
> SUID root thing (or creating a "help program")?

No. None of that is required for me on any kernel - Gentoo or Vanilla.
I just set up realtime-lsm and then run with realtime capabilites. I
would suggest that you use QJackCtl to run Jack as it will save your
settings nicely for you and give you patch bay access to hooking Jack
apps up to the server.

Note that I use pretty expensive RME cards. They work exceedingly well
for me. There are a lot of people out there that report they never go
faster than 128/2 or 256/2. 256/2 is about as good as any of my
Windows systems have every worked, and better then Pro Tools worked
when I owned it. You should not think that going a bit slower is
necessarily a problem. If you cannot hear the latency it doesn't
matte, and even if you can hear it, you can nudge recorded tracks
after recording to get a better sound if you can lay down a good
track.

>
> Any more thoughts?

Yes, but not sure you're going to like them... ;-)

The first one is easy. Try some different Jack settings. Instead of
128/2 try 64/4, or 128/3, etc., and see if some other setting works.
You might get the same latency, or you might have to go a bit slower.
The only time I actually use low latency is when recording. It's never
needed for playback only. Most of the time I run 512/2 just to ensure
no xruns causing clicks in my work.

On my 32-bit machines I've always been able to run Jack the standard
Gentoo-sources  kernel and get good realtime results. I have had to be
careful about what options I choose, and on a couple of machines
different kernel options have caused xruns (such as networking) but
I've always managed to get it to work and work well. Sometimes it has
taken some time, but it has worked. Maybe we need to look at how you
are configuring the kernel. Possibly send your config file off list or
I'll send you one of mine.

That said, on my new AMD64 machine gentoo-sources just doesn't cut it.
I had to go to a custom kernel to get realtime to work. I first tried
ck-sources, which lots of people report as working for them, but that
did not work for me, so I went with Ingo's realtime preempt patches
and I'm getting pretty good results. I get a few xruns/day at 64/2,
none so far at 128/2 running 20 track sessions in Ardour. I'm using
2.6.14-rc4-rt1. Here's the patches required to do that, should you
choose to go there:

http://kernel.org/pub/linux/kernel/v2.6/linux-2.6.13.tar.bz2
http://kernel.org/pub/linux/kernel/v2.6/testing/patch-2.6.14-rc4.bz2
http://redhat.com/~mingo/realtime-preempt/patch-2.6.14-rc4-rt1

(This one is VERY new. There are more stable, tested versions out
there based on 2.6.13. I needed this due to AMD64)

Once this is up and running you get access to setting priorities for
all devices and things work pretty well. (I.e. - don't be disappointed
if it doesn't do any better the first time you boot it.)
Unfortunately, since Gentoo doesn't support an 'audio kernel' yet you
and I would have to manage updates on our own. That said, this is the
way most people interested in good realtime performance have gone.
Maybe I've just been excessively lucky up until now.

It's probably worth it to review how you've set up realtime-lsm one
more time, just in case, and possibly to look at your hardware setup a
bit.

lspci
lsmod
cat /proc/asound/cards

>
> Thank you for all your help!

Wish it was more successful. We should just keep plugging away.

What audio stuff are you going to use this machine for, BTW?

- Mark

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