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

[Jan Depner]

On Sun, 2004-02-22 at 14:39, Eric wrote:
> 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...
> 
	The short answer is yes.  Get an AGP card.  You can also adjust the max
latency on the PCI bus (including the AGP latency).  I do this on my
NVIDIA card.  Take a look at my page for info on this -
http://myweb.cableone.net/eviltwin69/ALSA_JACK_ARDOUR.html
In addition you need to check your IRQs.  Using the Delta 66 you don't
need to set your sample size smaller since you can use the digital mixer
on the card to monitor your recording with basically zero latency (see
envy24control).  Ardour will adjust for the sample size.  I always
record with sample size of 2048 (I have a DSP2000 - same chipset) since
it's less load on the system.



> 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.
> 
	XFS should be fine.  For best results it should be on a separate
filesystem.  You should also use ramfs.  Don't use ext2 or ext3.  Use
reiserfs or XFS for your data drive.  Again, more info on my web page.


Jan