Sat, 13 Jan 2001 frank mori hess wrote:
> Hello,
>
> I saw some discussion about problems with video cards introducing latency
> into real-time tasks, so I thought I would contribute my experiences in
> the matter. I used rtlinux 3pre9 on 2.2.17 kernel, and my usual timing
> error (from the examples/measurements test) is about 10usec.
>
> Using XFree86 3.3.6, I tried three different cards,
>
> PCI Trident 3dimage 9750: Scrolling in an xterm caused timing errors to
> increase to about 50 usec. Dragging the xterm around the screen or
> opening/closing windows caused errors of a few thousand usec.
>
> AGP Cirrus Logic CL-GD5465:
> Dragging around and opening/closing windows would cause occasional
> timing errors of up to 1000 usec.
>
> AGP SIS 6326:
> No problems observed.
>
>
> Setting the "no_accel" option in XF86Config made any timing problems
> disappear.
This looks like the dreaded command FIFO stalls... (AFAIK, there hasn't been
IRQ related issues with XFree86 for ages.)
I thought this happened only with XFree86 4.0.x (which has FIFO full checks
disabled by default), but apparently this is not the case. Is there such an
option for 3.3.6 as well, and if so, is it possible that you have it disabled
on your installation? It could be a compile time switch...
(The reason why a distro would have the FIFO checks disabled is to get better
X benchmark results. See my previous post.)
//David
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