[PATCH] Ensure blitter quiescience before reading pixels from the framebuffer

Michel Dänzer michel at tungstengraphics.com
Mon Jul 30 23:36:36 PDT 2007

On Tue, 2007-07-31 at 09:09 +1000, Daniel Kasak wrote:
> On Mon, 2007-07-30 at 19:02 +0200, Michel Dänzer wrote:
> > Not sure there's still anyone around who cares about XAA...
> As others have noted, XAA is all we've got at present. 

That's just not true, but note that the above doesn't say anything about
the relative merits at all. It just points out that there's currently
nobody (that I know of) actively looking after XAA, as an attempted
explanation for the lack of response to Bernardo's patch. As you guys
don't seem happy with this situation, somebody should step up.

> Having said that, I appreciate that work is going on with EXA. In 
> particular the zero-copy GLX_EXT_texture_from_pixmap stuff for my r300 
> does wonders for beryl / compiz, and I'm certainly grateful for this 
> and any other work done, but in all honesty, this is a corner case ( 
> albeit a very nice looking one ). While it makes compiz smoother, it 
> ( EXA ) also slows down actual rendering of apps by an order of magnitude. 

Define 'actual rendering'. I haven't noticed anything that's
significantly slower with EXA than XAA with a compositing manager, have

> Sure, a compositing manager on top of this largely hides this fact, [...]

That's a funny statement, given that improving performance with a
compositing manager is one of EXA's main goals.

> > > On xf86-video-intel 2.1.0 with Beryl / Emerald drawing everying, XAA is still way
> > > faster then EXA. Noticable - like 5x faster w/ EXA on a Core 2 Duo MacBook.
> I've found this too, and not just with a composited desktop. Running
> Enlightenment with the XRENDER backend and EXA gives me about 1 fps with
> 100% CPU load with relatively mildly animated backgrounds ( I845G
> video ) - which run effortlessly at 30fps and low CPU load otherwise.

Unfortunately, this kind of anecdotal evidence isn't nearly as useful as
the detailed analysis done by Carl Worth, e.g.

> > > On my girl's Sony Vaio with just a Core Duo @ 1.66 GHz the same Intel driver
> > > (just built for 32bit of course) is so slow, that it just draws 1fps with EXA when
> > > you scroll in kpdf, abiword etc. while with EXA it is usable, most of the time.
> > 
> > For a GLX compositing manager, you need zero-copy
> > GLX_EXT_texture_from_pixmap which is only available in the xserver GIT
> > master branch (and only with the Mesa GIT master branch driver i915tex
> > for this hardware so far).
> I've also been trying to get this working. If I set the Legacy3D option
> to 'false', I get:
> no GLXFBConfig for default depth
> this isn't going to work ...

You're probably hitting
https://bugs.freedesktop.org/show_bug.cgi?id=9264 , can you try the Mesa
patch attached there?

Earthling Michel Dänzer           |          http://tungstengraphics.com
Libre software enthusiast         |          Debian, X and DRI developer

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