By Luck, Marek Discovers A "Serious Performance Fix" For RadeonSI
Hitting the Mesa mailing list this afternoon was a RadeonSI patch to disable ReZ. His comment was simply, "This is a serious performance fix. Discovered by luck."
In the patch a code comment he added warns, "DON'T USE EARLY_Z_THEN_RE_Z !!!" He found this code caused a performance decrease of 15% with DiRT Showdown on ultra quality settings.
By deleting this case of using EARLY_Z_THEN_RE_Z, this small patch allows for better performance. This should also help other Linux games on RadeonSI making use of complex shaders.