Present in the Linux 4.7 kernel and thus far in the Linux 4.8 development cycle has been a significant performance regression affecting the Radeon R9 290 and other select GPUs. This performance drop has been very noticeable and I’ve seen it since Linux 4.7-rc1 while finally an independent user went through the process of bisecting the kernel to find the problematic commit of this hefty performance drop…

Source: Phoronix – That Radeon Performance Regression For R9 290 & Co Might Be Nailed