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Where to realize a hardware cursor depends on where on the screen it will be displayed. For example it only needs buffers for the cursor plane on a certain GPU if it overlaps with a monitor that is connected said GPU. Previously, we were too eager with uploading the cursor plane buffers, which in effect resulted in the secondary GPU always being woken up when changing the cursor, even though the cursor plane would actually never be set unless the pointer cursor was moved to a monitor connected to the secondary GPU. These wake-ups caused noticable stuttering; thus by uploading the buffers more lazilly, the stuttering is avoided. Closes: https://gitlab.gnome.org/GNOME/mutter/issues/77