Slow AA and RGB text rendering

[Michel Dänzer]

First of all, this went to the wrong mailing list; debian-x is for
discussion of the Debian X packaging. I'm CC'ing the upstream xorg list,
please follow up there only.


On Wed, 2006-01-25 at 22:30 -0500, debian at openserve.org wrote: 
> 
> On the following machine:
> Athlon64 3000
> Nvidia GeForce 6600GT
> Kernel 2.6.14, Xorg 6.9.0.dfsg.1-3
> (Render enabled and verified working, Composite disabled, GLX working) 
> 
> I'm getting only 22 kchar/s using:  x11perf -rgb10text
> Even software rendering should not be THIS slow considering that...
> 
> ..For comparison, I dug out a retired P2-266 laptop with a PCI S3 
> video chipset.  It hasn't been updated for years. (Kernel 2.6.1, 
> XFree86 4.2.1-16)  The same benchmark reported about 17 kchar/s.

Things to consider:

      * -rgbXtext (I assume this is subpixel AA) is very non-trivial to
        accelerate, I'm not aware of any accelerated (and correct)
        implementation yet.
      * Hence this test probably boils down to software rendering, which
        is usually limited by the CPU access to video RAM.
      * CPU reads from video RAM are still about as slow as ever
        (especially with AGP, less so with PCIe).


> [Sidenote: for some reason x11perf -aa10text is not working in 6.9.0.. 
> it still does RGB and reports the same result.  Otherwise, I would 
> have reported this as well.  Nevertheless, my guess is that the 
> result would be the same, judging by perceptible text redraw speed in 
> applications with AA vs RGB mode.]
> 
> Also, for reference, my prior Radeon 8500 card gave similar poor 
> results.  Before Xorg 6.9.0, I got around 45-50 kchar/s in either AA 
> or RGB mode using x11perf -aa10text or -rgb10text respectively.  
> While this sounds much faster, it is nowhere near what it should be 
> and still results in visibly sluggish text redraw.  I used to get 
> around 250-300 kchar/s with AA text in some older XFree86 releases 
> (and one CVS checkout of pre-6.8.2 Xorg!)  with varied Radeon 
> hardware. (RGB was still slow, around 50 kchar/s)

Some of these oddities might be explained by the fontconfig
configuration on your system. E.g., if your fontconfig configuration
enables subpixel AA, that seems to apply to the -aaXtext tests as well.
Some of us used to get fooled in the other direction because fontconfig
silently chose a non-AA font for -aaXtext, so we got impossibly high
numbers for that.


-- 
Earthling Michel Dänzer      |     Debian (powerpc), X and DRI developer
Libre software enthusiast    |   http://svcs.affero.net/rm.php?r=daenzer