[Bug 27069] OpenGl is slower on dri2

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=27069

--- Comment #3 from Stefan Dösinger <stefandoesinger at gmx.at> 2011-09-01 16:20:12 PDT ---
This problem still exists, UMS(as far as 3D is still working with it) is much
faster than KMS. Unfortunately the only app that's still working with UMS in
Mesa 7.11 is glxgears.

On my r250 GPU glxgeares runs at 2600 fps with UMS, 1070 with KMS(default
Window size). At 1400x1050 the numbers are 370 fps(UMS) and 60 fps(KMS).

I don't think vsync causes the issue, disabling it seems to work fine, at least
for windowed apps.

etracer is still a lot slower with KMS than it used to be. At 1400x1050 and
otherwise default settings it runs at 15-20 fps. With an ancient Mesa version I
tested today(6.4.2) it runs at a pretty okish 60 fps at the same settings.

The problem seems to be on the GPU side. Whenever the problem occurs the CPU is
idle and the GPU working, and increasing the rendering resolution makes the
problem worse. The unfortunate situation this creates is that the 6 years old
Mesa on my old hard drive vastly outperforms Mesa 7.11 in many rendering
situations.

I could not spot any CPU side problems, but the GPU slowness makes it hard to
test. My unscientific guess is that in setups where the KMS GPU slowness
doesn't matter Mesa 7.11 is about 50% faster than Mesa 6.4.2. (etracer with a
tiny resolution, long view range and lots of objects)

I'll test r300 on a Radeon X1600 GPU over the weekend. This GPU/driver combo is
pretty slow as well, but I'm not sure if r300 still supports UMS.

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