R600 Gallium3D LLVM Compiler Back-End Benchmarks
Written by Michael Larabel in Mesa on 14 July 2013 at 12:31 AM EDT. 6 Comments
In the past few days after having delivered R600 Gallium3D benchmarks of the R600 SB back-end that is a new shader optimization back-end for the Radeon Gallium3D driver, here's some comparison benchmarks against the upcoming R600 LLVM back-end.

The R600 SB back-end that's found with the upcoming Mesa 9.2 isn't enabled by default (it requires setting the R600_DEBUG=sb environment variable), since AMD developers view the R600 LLVM back-end as the future. The LLVM back-end is more versatile and it's needed for the Gallium3D OpenCL/GPGPU compute support. AMD's Tom Stellard has been working heavily in this back-end over the past two years.

This GPU back-end was merged into LLVM 3.3, which was released last month, and can be built with Mesa 9.2 using the appropriate compiler switch. The LLVM back-end can then still be dynamically toggled with the R600_LLVM environment variable.

For this early Sunday benchmarking are tests from a mid-range Radeon HD 4000 series GPU in its stock configuration, with the R600 LLVM compiler back-end in use, and then when the R600 LLVM compiler back-end was disabled but the R600 SB optimizations enabled.

The benchmark results in full for this testing can be found on OpenBenchmarking.org in 1307102-SO-MESA92RAD62. Benchmarking happened from an early Ubuntu 13.10 installation with the Linux 3.10 kernel. (Note: the CPU frequencies were maintained the same throughout testing but ignore the frequency differences in the system table due to the Intel P-State driver in recent Linux kernels reporting bogus values for some CPUs.)

Viewing the rest of the results show that enabling the R600 LLVM GPU back-end can lead to a boost in the open-source AMD Linux driver's frame-rate, but still for Mesa 9.2 the R600 SB optimizations can lead to greater frame-rates in the range of Linux OpenGL games that were tested.

About The Author
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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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