[Bug 8938] [ATI/radeon] Xv tearing

bugzilla-daemon at annarchy.freedesktop.org bugzilla-daemon at annarchy.freedesktop.org
Thu Nov 30 16:51:48 PST 2006

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------- Additional Comments From sroland at tungstengraphics.com  2006-11-30 16:51 -------
(In reply to comment #24)
> Patch made things slightly better, but again not very good. The hangs are gone
> (at least for the test movie I have), but the tearing is still present.
> The tearing is now also very funky. Since it is a planar format, I constantly
> get the luma and chroma out of sync. Looks like some mushroom bearing hippies
> have invaded my machine. :)
> From my point of view, there are three unanswered questions (which might all be
> related):
> 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... 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

> 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.

> 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.          
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