What about GPU perf counters?

Regarding the "Infrastructure for tracking driver performance events"
patch article listed later on the LWN kernel page... Why intel GPUs (or
just that particular GPU?) don't have performance counters? Or if they/it
actually do have them, could this perfcounters thing expose them in
addition to the CPU counters?

It would be pretty important information for anything 3D related, maybe
even just for today's composited Desktops.