[Bug 30679] KDE editor sluggish from f8fb9312d791af1f77020e8c2d35bb30841ed9aa

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=30679

--- Comment #8 from Karl Tomlinson <bugs.freedesktop at karlt.net> 2010-10-10 15:15:31 PDT ---
There is a reasonable amount of region work in the samples.

Given PolyText16 is used here, I wonder whether the DamagePendingRegion
is quite complex, which could make its intersection with CopyReg in
exaCopyDirty complex, leading to multiple DownloadFromScreen calls.

Option "EXAOptimizeMigration" "off" in the Device section seems to workaround
the issue.

Perhaps the (RegionNumRects(pValidDst) > 10) path or similar could also
be used when RegionNumRects(pending_damage) is large.

On the driver side, DFS could perhaps skip the GPU blit for small rectangles,
or maybe consider moving the BO to GTT.

The way to get best performance for this particular case I think would be to
modify the EXA/driver ABI so that EXA can indicate to PrepareAccess (or equiv)
that it only needs write access.
However, I suspect that would require significant auditing and perhaps
refactoring of EXA and likely other DIX to know which operations are
write-only.

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