LCA: Two talks on the state of X [LWN.net]

LCA: Two talks on the state of X

Posted Feb 14, 2008 12:45 UTC (Thu) by nix (subscriber, #2304)
Parent article: LCA: Two talks on the state of X

I hope video overlays don't get completely removed. On my 9250, I see 5% CPU usage when
rendering full-screen full-motion video through Xv (mostly because of rescaling): I see >80%
CPU usage at about five frames a second if I'm using textured video playback, even with the
DRI to help out.

Obviously, I never ever use textured video playback. My preferred window manager doesn't
support compositing, and even if it did, I'm obvously staid and conventional in actually
*watching* video when it's playing rather than spinning it around and applying bling to it.

Yes, the 9250 is a bit old, but it's not *that* old, and the main CPU (an Athlon 4) is not
*that* old either. It would be bad to require everyone to upgrade to video cards requiring
non-free drivers (or a new motherboard: Intel cards or cards on PCIe) just because of an
architectural revision to enable video playback to interoperate with features that are of much
less importance than actually playing back the video at reasonable speed.

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LCA: Two talks on the state of X

Posted Feb 14, 2008 15:09 UTC (Thu) by daenzer (✭ supporter ✭, #7050) [Link]

As the xf86-video-ati radeon driver doesn't provide a textured XVideo adaptor yet, I assume
you're referring to using an OpenGL output plugin in your video player. The reason this
performs so badly is that the Mesa r200 driver is very inefficient in getting texture data
from the application to the GPU, involving several memory copies and possibly other
processing.

A textured XVideo adaptor (as implemented in xf86-video-intel e.g.) shouldn't require
significantly more CPU cycles than an overlay.

LCA: Two talks on the state of X

Posted Feb 15, 2008 9:20 UTC (Fri) by ranmachan (subscriber, #21283) [Link]

A textured XVideo adapter could also have the advantage that you can play more than just one
video at the same time.  NVidia had that ages ago in their binary driver (because their cards
could do the color conversion on stretchblit AFAIK).

LCA: Two talks on the state of X

Posted Feb 15, 2008 21:13 UTC (Fri) by nix (subscriber, #2304) [Link]

How... useful.

Do you have a multistreamed consciousness, or something? How on earth can 
you pay *attention* to two videos at the same time? (And if you're only 
paying attention to one, isn't the other one annoying, flickering away in 
the background?)

LCA: Two talks on the state of X

Posted Feb 19, 2008 7:20 UTC (Tue) by daenzer (✭ supporter ✭, #7050) [Link]

Think several browser tabs with embedded video players. Only one of them may actually play at
any time, but only one of them can get the single overlay port.

LCA: Two talks on the state of X

Posted Feb 19, 2008 7:55 UTC (Tue) by nix (subscriber, #2304) [Link]

Argh, yes, I see, because they won't even display a paused image without 
an overlay.

LCA: Two talks on the state of X

Posted Feb 15, 2008 21:16 UTC (Fri) by nix (subscriber, #2304) [Link]

I completely failed to realise that Xv could turn the incoming video into 
textures and slam it at the video card. Obviously if it did that things 
would be about as fast as slamming it at the video card without 
texturizing it first, with the advantage that modern cards are designed to 
render big textures fast.

And, yes, if the thing's doing copies performance will suck. From your 
wording it sounds like it's not something fundamental to the hardware :) 
When I get another machine to use as a desktop box later this year (so can 
afford to restart X on this one without losing all my working state) I 
might have a look at that. Someone else will probably get to it first, 
though...