[vdr] PCI fun (RGB/PAL over VGA at variable frame rate)
art_k at o2.pl
Sun Aug 17 03:41:18 CEST 2008
Gavin Hamill wrote:
> Over the last days, Thomas and I have been trying to sort out why my
> nearly-identical machine couldn't run his VGA sync patches properly.
> The key difference is my Radeon 7000VE is PCI, whilst his is AGP. I
> tried the PCI Radeon in two old Pentium-3 era machines, and on my modern
> Pentium D930 desktop, all with the same behaviour - fullscreen video
> over PCI causes huge CPU usage in the Xorg process, even when using xv
> When I switch the PCI Radeon for a PCI Express X300 (the very lowest 'X'
> series you can get), everything is glorious: Xorg CPU use is barely 1%.
> Unfortunately I don't have any machines with both AGP and PCI on which
> I can try the same OS image but we both think it's safe to conclude that
> PCI is just unsuitable for this task.
PCI in general should be perfectly fine, for SDTV at least.
While displaying SDTV (vdrsxfe) I see ~20% cpu use for X on AGP, ~44% on PCI
(same machine, different heads, AGP is MGA450, PCI is MGA200).
The huge difference is likely due to something else, like
- display (X) driver (but even drivers which just memcpy the video
data to the (xv) framebuffer should work on a modern machine)
- PCI chipset (eg I had a VIA-based mobo, and it couldn't even keep up
with SDTV on a PCI head, swapping the mobo for one w/ a real chipset
made all problems suddenly disappear...)
You could probably do some setpci tweaks to improve PCI throughput, but
I doubt the gain would be enough (I'd expect 10% improvement or so).
More information about the vdr