Intel Continues With Mesa Changes For Valve
Written by Michael Larabel in Valve on 7 August 2012 at 03:06 PM EDT. 22 Comments
Intel open-source developers continue to make changes to Mesa at the request of Valve Software's Linux team.

Following the recent article about Valve & Intel Work On Open-Source GPU Drivers, hitting the mailing list for Mesa development today was a set of patches by Intel's Eric Anholt with changes at the request of Valve.

The patch-set comes down to exposing more information than what is currently exposed through the GL_ARB_debug_output extension. Some of the information now exposed through the performance debug information include messages for freagment and vertex shaders triggering register spilling, GPU stalls waiting for a query object, advice to using a blit call for avoiding a stall on glBufferSubData(), stalling the GPU within glBufferSubData(), mapping a busy buffer object, failing to fast clear depth, notice on recompiling shaders, the state cache size limit being exceeded, and notice for stalls during shader compilation.

These performance debugging messages can benefit any OpenGL game/application developer, but are just available at this point for the i965 DRI driver and does require setting INTEL_DEBUG=perf.
One of Valve's requests was for GL_ARB_debug_output for performance traps they should know about. Unfortunately, Mesa's ARB_debug_output support is very limited at the moment, so this just gets messages in place, which we can convert to GL_ARB_debug_output at some later time.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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