When running env INTEL_DEBUG=perf gnome-shell ... on an Intel system (i7-7700) I see constant warnings seemingly every frame:

Moving the mouse

CPU mapping a busy "isl-miptree" BO stalled and took 0.346 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.364 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.348 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.357 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.331 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.355 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.335 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.363 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.351 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.343 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.355 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.333 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.319 ms.

Window maximize animation

CPU mapping a busy "isl-miptree" BO stalled and took 3.075 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 1.852 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 1.485 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 1.258 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 1.488 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.318 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 1.954 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 1.965 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 2.281 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.308 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 2.824 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 2.765 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 2.888 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 0.324 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 3.324 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 3.212 ms.
CPU mapping a busy "isl-miptree" BO stalled and took 3.342 ms.

These all seem to go away using !189 (merged), but I'm logging this as a separate bug in case it's possible to solve without !189 (merged).