[linux-audio-user] dipping toes in 2.6 waters

[Fernando Pablo Lopez-Lezcano]

On Sun, 2004-08-08 at 15:05, Fernando Pablo Lopez-Lezcano wrote:
> On Sat, 2004-08-07 at 16:17, Lee Revell wrote:
> > On Sat, 2004-08-07 at 18:50, John Check wrote:
> > > On Saturday 07 August 2004 06:30 pm, Lee Revell wrote:
> > > > I recommend disabling all hardware video acceleration when tuning a
> > > > system for low latency (set Option "NoAccel" and commend out the "dri"
> > > > line).  This will prevent X from interacting directly with your hardware
> > > > - it is complicated enough when only the kernel can access hardware.
> > > > Then, once you get that working, re-enable 2D acceleration, then DRI/3D
> > > > acceleration, if these do not cause problems.  This will make it much
> > > > easier to get the problematic video drivers fixed.
> > >  
> > > Definitely a good strategy, but nobody is going to take a system with no
> > > video acceleration seriously.
> >
> > Yes, of course this is not a long term solution.  The point is to get
> > the buggy video drivers fixed (this is open source after all), in order
> > to do that we need to be able to say 'when i enable DRI with $FOO
> > driver, I get xruns, and these go away when I disable it'.
> 
> Here's one case. 2.6.8rc2-mm2 + voluntary O3, 

Still the same result on rc3, voluntary O4...
Will test soon on rc3/O5.

Anything else I can do to better debug these latency spikes?
(they also probably happen in the mga and r128 drivers)
-- Fernando

> lsm module, kernel config
> files derived from current default FC2's, very recent alsa CVS (post
> 1.0.6rc2), FC2, xorg, gnome desktop, P4 laptop 1.7GHz/512M with Radeon
> video chipset and Intel Corp. 82801CA/CAM AC'97 Audio Controller,
> kernel_preempt=1, voluntary_preempt=3, acpi=on (sound does not work with
> acpi=off), irq's left in default state[*]
> 
> With "Option NoAccel" and an idle jack in an xterm (-p128 -n2), start
> glxgears, move the window around and there are no xruns (any size
> window).
> 
> With acceleration enabled, start glxgears and with the default size move
> the window around, no xruns. Enlarging the window (this is on a
> 1600x1200 screen) eventually triggers tons of xruns when the window is
> moved and is "large enough". 
> 
> Samples of output from jack:
> 
> **** alsa_pcm: xrun of at least 7.470 msecs
> **** alsa_pcm: xrun of at least 7.401 msecs
> **** alsa_pcm: xrun of at least 7.438 msecs
> delay of 5728.000 usecs exceeds estimated spare time of 2644.000;
> restart ...
> **** alsa_pcm: xrun of at least 7.482 msecs
> **** alsa_pcm: xrun of at least 7.216 msecs
> **** alsa_pcm: xrun of at least 7.476 msecs