[Bug 8938] [ATI/radeon] Xv tearing

bugzilla-daemon at annarchy.freedesktop.org bugzilla-daemon at annarchy.freedesktop.org
Thu Nov 30 23:40:54 PST 2006

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------- Additional Comments From drzeus-bugzilla at drzeus.cx  2006-11-30 23:40 -------
(In reply to comment #26)
> (In reply to comment #24)
> > A. Why is there a bandwidth issue and where? There should be enough bandwidth
> > over both the PCI bus and internally on the card.
> Not sure. You said that mtrr are correct, so there doesn't seem to be many
> possibilities left. What sort of chipset is that? There exist indeed some which
> have a very weak pci implementation where you can hardly expect more than
> ISA-like performance...

I recently changed motherboards on this machine, and the problem was on both.
The previous board was an Intel based (unsure exactly which chipset), and the
new is a VIA VT82-something.

> The card could be problematic, there exist versions with
> only 64bit sdr ram, while in theory those 10MB/s you need to upload the video
> aren't really much things tend to fall apart with those cards if they are too
> bandwidth-limited.

This is a Radeon 7000, which according to wikipedia is one with only 64-bits for
the memory bus.

> > B. Why is there such a speed difference in pushing data to the AGP card (over 10
> > times as fast). AFAIK, the AGP bus isn't that much faster, especially on such an
> > old machine as this.
> It shouldn't be that much faster, then again there are strange slowdowns with
> dri with pci rv250-like chips, way beyond what you'd expect (say factor 5 or so,
> even when compared to AGP 1x). That is probably a different problem though as it
> seems related to the cp fetching things over the pci bus, which shouldn't be an
> issue here.

Also, DRI is disabled here.

> > C. Why am I getting tearing when I have XV_DOUBLE_BUFFER set to 1? Shouldn't
> > there be a cache of at least one image on the card that we flip to?
> Not sure. Looks like it shouldn't happen. Maybe a frame could be completely
> missed so you'd upload a new frame to the current buffer.

Any way to determine what's going on here?          
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