[ardour-dev] Latency: AGP vs PCI video card and XFS journalling vs not

[Eric]

I have built a box that I thought would be able to support some very
low-latency recording in the eventual hope of software monitoring with
some effects in the loop (is anyone able to do this?).  It's a dual
athlon 2400 w/ 1GB of DDR266, dual 10K SCSI drives, and my M-Audio
Delta66.  I'm using the Debian unstable packages (jack 0.94 and ardour
beta9+3) with a 2.6.3 kernel and have played around w/ all the
standard latency issues (no extra stuff running, swapped PCI cards
around for interrupts, etc.).  However, I'm not able to go lower than
the default jack 3 periods of 1024 (with rt enabled, obviously) when
working on my typical projects of 8-12 48KHz mono tracks, even without
any effects in the loop.  It is dissapointing to have to go back to
hardware monitoring w/ no effects...I have two questions:

1.  Could it be my old Voodoo3 PCI video card is hogging the bus?
Rendering the mixer window definitely has an effect on my audio...if I
drag it around or minimize/maximize it I can actually slow down the
audio playback (which was surprising to me) or cause xruns and
timeouts.  I've taken to just minimizing everything while I'm
recording.  I didn't care about my graphics card, but now I'm
considering an AGP one (nVidia GeoForceFX 5600 or ATI Radeon 9700)
just to try and improve this...

2.  Could it be my XFS filesystems?  If I have 8 or so tracks on one
drive, it can't even handle playback w/o giving disk errors.  I've
tweaked all the XFS options, and currently have a large (64MB) log for
each filesystem that resides on the opposite disk.  Would turning the
log size up or down help?  Is there a way to just turn off journalling
in XFS, or would ext2 be better?  I did notice that exporting to my
default param (i.e. small log) ext3 root partition seems to be faster
than to my XFS.

-- 
http://ir.iit.edu/~ej