[ardour-dev] Ancient history? - Problem identified

[David Gatwood]

On Nov 11, 2004, at 9:38 AM, cv223 at comcast.net wrote:

> A few days ago I posted the following message about tracking down 
> xruns using Ardour to record to a SCSI Raid0.  At the end of the 
> message, I asked whether anyone had any ideas about why commenting out 
> a single line in streamview.cc (which at the very least eliminates 
> updating the "progress" rectangles during recording) completely 
> eliminates my xrun problem, in a rather dramatic fashion (dozens of 
> xruns per min to none).  Since I got a goose egg in response, I 
> thought I would try again because I've run out of things to test and 
> don't know where to look next. 

I'd look at the video drivers.


>   Basically, how can display updates in Ardour during recording cause 
> xruns with writes to the hard drives?

If the video driver holds interrupts off for too long, all sorts of 
juicy things can happen.  Look at the driver and see if they do 
something stupid like doing a large bcopy/memcpy in an interrupt 
handler.  If so, slap the driver author on behalf of everyone who has 
ever written a driver.  :-)  Then, buy a video card that uses a 
different driver.

That or you could be sharing an IRQ between the video card and your 
audio card or something.  I know that shouldn't make a difference in an 
ideal world, but sometimes it does.

A final, rather gross possibility is that you may be running into a 
memory bandwidth issue.  AGP devices have serious DMA access to main 
memory and can hog access to memory for long periods of time by their 
very nature.  It's possible that the device is causing enough latency 
that the CPU can't keep up..  Have you tried increasing the audio 
card's buffer size?  Does your X server have acceleration support for 
your video card?  Do you know if your card have any performance tuning 
capabilities?  Possibly a way to throttle its bandwidth consumption?

Just some random thoughts.


David