Subject: Re: [linux-audio-user] Advice needed re: latency tuning/optimization, esp. video
From: Robert Jonsson (robert.jonsson_AT_dataductus.se)
Date: Mon Feb 16 2004 - 21:15:31 EET
Hi,
måndagen den 16 februari 2004 19.24 skrev Chris Metzler:
> Hi. I'm looking for some advice on how to deal with latency introduced
> by graphics activity.
>
> My setup:
> AMD Athlon XP 2000+
> ASus A7V333 Raid+ Motherboard
> 1 GB Corsair CAS2 PC2700 RAM
> Creative SBLive 5.1 sound card
> Matrox Millenium G550 video card, AGP4x, 32MB RAM
> 1 WD800JB IDE disk (80 GB, 8 MB cache); 4 WD1200JB IDE disks (120 GB,
> 8 MB cache each)
> Kernel 2.4.23 + preempt + lowlatency, XFree86 4.2.1
To summarize, your system should rock.
<...>
> The sound card shares IRQ 10 with the USB2 bus; but I have no USB
> devices of any sort. On IRQ 9 are two of my four IDE channels.
This is probably not optimal, if I understand correctly irq10 is a bit down in
the priority list, if you haven't read the lowlatency howto, do that.
<...>
> This result surprises me. I'm using a video card that's supposedly
> very very good at 2D stuff -- indeed, it's the video card that RME
> recommended as recently as last year as their card of choice for
> audio workstations. It's definitely open at AGP 4x (XF86 wants to
> open it at 1x unless you explicitly say in the config file that you
> want 4x). 32 MB isn't a huge amount of video RAM, but I would think
> would be fine for 2D stuff.
That a card is good for graphics doesn't necessarily mean that it's good for
audio. That RME recommends it points to that the card should be well behaving
hardware wise. Things to check:
- That it has an irq that has lower priority than the audio card ... might not
be possible with agp ?
- Try and change the AGP setting. Faster isn't necessarily better.
The most probable offender is the driver though, I don't know if there are
multiple drivers for this card so you could try another?
If you have a graphic login (e.g. you login directly to X) you should check
that xdm/kdm or whatever display manager you are running does not have
elevated priority. Mandrake does this as has been noted here before, for
mandrake it's in:
/etc/X11/xdm/Xservers
the line is
:0 local /bin/nice -n -10 /usr/X11R6/bin/X -deferglyphs 16
-10 is wrong 0 is _more_ right.
If you are running KDE or GNOME there might be issues with certain functions
of the desktop environment. I'm running KDE myself with no problems but
others have reported problems with both.
I guess you could try different graphical settings also, amount of colors,
display size... no solutions but it might help to identify the perpetrator.
All I can think of right now. Hopefully someone with a similar card/setup can
comment with better ideas.
/Robert
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