Major Performance Breakthrough Discovered For Intel's Mesa Driver
As shown by my most recent tests of Windows 8.1 vs. Ubuntu 14.10, Intel's Windows OpenGL driver is still largely faster than their open-source Linux driver. LunarG has been exploring the performance issues with the Intel Linux driver via their contract with Valve Software for making graphics drivers better for Linux gaming. In their research and testing they found a fundamental reason why the Intel Linux driver runs slower than the Windows driver.
Jens Owens of LunarG shared the basic information on the storage of the big performance gain in Intel's Mesa driver via a brief post.
The issue comes down to a difference in how hardware samplers were working compared to Intel's Windows driver. LunarG passed along their findings to Intel's Linux crew who with the help of their hardware engineers found a bit needed to make the hardware run faster. A patch to the Intel Linux kernel driver will then dramatically improve the performance. The levels we're talking about are 17~25% faster Left 4 Dead 2, 16~20% for Counter-Strike: Global Offensive, and Lightsmark by 60%.
While they went public today with this performance breakthrough, no patch is publicly available. Jens told me in an email that there are concerns that just setting this special bit and leaving it on isn't good enough as it could break some specific video acceleration functionality when enabled. The Intel crew is still working on a proper patch but there's no ETA when a production-ready patch will be available. Jens also confirmed in the email that this patch is only relevant to Haswell graphics hardware. Hopefully a patch will be ready for the Linux 3.19 merge window...