[Bug 26892] Performance regression r600 in KMS vs UMS

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=26892

--- Comment #8 from Ancoron <ancoron at chaoslayer.de> 2010-04-20 15:09:23 PDT ---
I'm also suffering from the massive performance degradation switching from UMS
to KMS. I just switched from KMS back to UMS using a Radeon X1550 with a single
1680x1050 head because the desktop effects are unbearably slow on that system
(and the setup is fine according to all logs).

I miss the high resolution VTs and the nice plymouth boot splash, but in the
end I have to get some work done, that's why I switched to Linux years ago.

And on another machine (Radeon HD4770) I too have this issue. I thought that
graphics card would be fast enough to display the KDE4 desktop cube animation
smooth enough but it feels like being somewhat around 15-20FPS and with UMS it
was as smooth as it can get I think even under high workloads. With KMS however
the CPU workload influences the graphical performance of the system much more
than it does with UMS. Although this is a very subjective thing I'm sure it
would be measurable.

Both machines I currently use show this issue with kernels 2.6.32+drm33 (ubuntu
lucid), 2.6.33 and 2.6.34-rc4.

So this is a basic issue for KMS, regardless of the actual GPU chip. As I
regularly look at the performance measurements over at phoronix I see that KMS
focusses on the more complex work, rather than making the simple things faster
(that's an explanation why glxgears on my HD4770 runs about 500% faster with
UMS).

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