[Mesa-dev] i965: slow glTexSubImage2D because of Y tiling

[Alexander Monakov]

Hi,

i965 texture fast upload path did not work in 9.2.x due to this tiling
change, but was improved for 10.0 release series; however, you need to
use GL_UNSIGNED_BYTE format rather than GL_UNSIGNED_INT_8_8_8_8_REV to
hit it.  With that, upload on 10.0.x should be almost as fast as on
9.1.x.  Funny that upload was quite fast with X-tiling on 9.1 even
when the fast texture upload path was not used.

I believe the reason is that reading the texture on the GPU is faster
with Y-tiling (better cache usage), and when a few people noticed the
upload speed regression it was too late.

Finally, please note that PBO-based glDrawPixels is no longer slow
after this patch (to appear in 10.1 release):

http://cgit.freedesktop.org/mesa/mesa/commit/src/mesa/drivers/dri/i965/intel_pixel_draw.c?id=279e8d264109303f0e8248ab4c3703c71f65983f

(primus switches to PBO glDrawPixels when detects it to be fast).

Cheers.

Alexander