https://bugs.freedesktop.org/show_bug.cgi?id=108917
--- Comment #6 from Nicholas Kazlauskas nicholas.kazlauskas@amd.com --- I suspect that Alex is right about this being similar to the cursor update issue - a large volume of color management changes through the full atomic commit codepath would likely be quite slow. The dc=1 to dc=0 comparison is good evidence supporting it as well.
Expanding the cursor path into a generalized plane update fast path would likely resolve the issue, but may be tricky to do right.