[Bug 93864] Performance degradation when one display is in rotation

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93864

--- Comment #2 from Chris Wilson <chris at chris-wilson.co.uk> ---
Well that was contrary to my expectations. The change should be to apply the
bbox of the damage rather than the individual boxes, which is beneficial when
they are approximately the same - worst case is a pixel damaged top-left and
pixel bottom-right. Tracking damage bbox per CRTC may be a compromise - that
would help the case of having a clock in one corner of the display and
rendering in the other.

However, I think that doesn't explain the result with both being rotated. I
wonder if there is not something fishy with the rotation code. Since this is is
a 915gm, it will have to create a temporary surface with which to do the
rotation as the source framebuffer will be much larger than the render pipeline
can handle natively. Similarly the source framebuffer will be larger than a
fence and so untiled - but the intermediate and final should be tiled.

There's enough oddity here that having a read through of a full-debug log would
be interesting. Could you recompile with ./configure --enable-debug=full and
attach an xz compressed Xorg.0.log of ~10s of the various setups? The
full-debug logs will be huge.

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