Intel's Mesa Driver Gets New Performance Patch
Intel's Mesa DRI driver received a new patch this weekend that's capable of enhancing the open-source graphics driver's performance for some OpenGL games.
The new performance-enhancing Mesa patch is by Kenneth Graunke and entitled i965: Implement CopyTexSubImage2D via BLORP (and use it by default).
CopyTexSubImage2D is now implemented via the BLORP rather than the BLT engine to work around limitations of the latter not being able to blit X-tiled buffers and between buffers of different tiling modes.
In terms of what this patch means for end-users of Intel hardware on Linux, the PlaneShift MMORPG game is much faster. Up to now the game has just run at around one frame per second on Intel hardware while chewing up nearly the entire CPU due to its use of Y-tiled depth buffers with CopyTexSubImage2D. This is a common issue to massively multi-player games.
Additionally, the Xonotic first person shooter with 4x MSAA anti-aliasing is now measured to be about 6.35% faster as a result of this single Mesa patch.
The patch, which adds just over 100 lines of new code to the Mesa i965 DRI driver, can be found currently on the mailing list until it reaches mainline Mesa hopefully in time for next month's Mesa 9.1 release.
The BLT engine has many limitations. Currently, it can only blit X-tiled buffers (since we don't have a kernel API to whack the BLT tiling mode register), which means all depth/stencil operations get punted to meta code, which can be very CPU-intensive.
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