drm/i915: Change GEM throttling to be 20ms like the comment says.
keithp didn't like the original 20ms plan because a cooperative client could be starved by an uncooperative client. There may even have been problems with cooperative clients versus cooperative clients. So keithp changed throttle to just wait for the second to last seqno emitted by that client. It worked well, until we started getting more round-trips to the server due to DRI2 -- the server throttles in BlockHandler, and so if you did more than one round trip after finishing your frame, you'd end up unintentionally syncing to the swap. Fix this by keeping track of the client's requests, so the client can wait when it has an outstanding request over 20ms old. This should have non-starving behavior, good behavior in the presence of restarts, and less waiting. Improves high-settings openarena performance on my GM45 by 50%. Signed-off-by: Eric Anholt <email@example.com> Reviewed-by: Jesse Barnes <firstname.lastname@example.org>