radeon EXA & fallbacks

[Benjamin Herrenschmidt]

I find radeon EXA fairly slow for a bunch of things, like scrolling the
list in evolution or even ls -lR / in gnome-terminal. I did a bit of
oprofile and I'm spending a lot of time in memcpy,
fbCompositeSolidMask_nx8888x8888C and fbBlt. I don't have proper
backtraces yet though.

I did some quick traces of the driver and it seems I'm getting a lot of
fallbacks due to:

R200CheckComposite: Component alpha not supported with source alpha
blending.

The typical kind of operations are:

Composite fallback: op Over,
                    src  0x106e0370:m fmt ARGB8888 (1x1 R),
                    mask 0x1068abe8:s fmt ARGB8888 (259x10),
                    dst  0x10ba3ea0:s fmt xRGB8888 (512x512),
EXA fallback at ExaCheckComposite: from picts 0x10685f20/0x106e3590 to pict 0x10685588

(btw. Eric, I added xRGB8888 to your list of pixmap type "names").

This is with gtk 2.8.3-1 from debian, xft2 2.1.7-1, pango 1.10.0-2,
using an aa font in both case (Bitstream Vera Sans Mono 7.5 for the
ls -lR test and Arial from msfonts for evolution).

My lack of knowledge of 3D engines hitting hard here, I'll let you
guys have fun figuring it out :)

Cheers,
Ben.