1. Computers
  2. Display Drivers
  3. Graphics Cards
  4. Memory
  5. Motherboards
  6. Processors
  7. Software
  8. Storage
  9. Operating Systems


Facebook RSS Twitter Twitter Google Plus


Phoronix Test Suite

OpenBenchmarking.org

Auto-Vectorizing LLVMpipe For Performance Gains

Mesa

Published on 03 June 2012 01:58 PM EDT
Written by Michael Larabel in Mesa
7 Comments

Here's a hint that may allow for some notable performance gains out of the Gallium3D LLVMpipe driver for multi-core systems.

Recently I wrote about the Gallium3D LLVMpipe Driver On LLVM 3.1. There wasn't really any major performance changes to note for this Gallium3D "software rasterizer" driver that uses the CPU and not the GPU as a means of fallback support, but this Sunday I received a message from Hal Finkel. This developer from the Argonne National Laboratory wrote the new basic-block auto-vectorization pass for LLVM 3.1. Below is the message he sent over to me regarding this work and LLVMpipe.
Michael,

I looked through your benchmark results on "Gallium3D LLVMpipe Driver On LLVM 3.1", and, as author of LLVM's new basic-block autovectorization pass, I wonder if turning on autovectorization would improve the 3.1 results.

If you're curious about the autovectorization pass, you can see my presentation at the developer's conference earlier this year: http://llvm.org/devmtg/2012-04-12/

It seems like llvmpipe uses its own pass manager, which is probably not a bad thing, but it is either intentionally minimalistic, or is pretty out of date (or both). There are many other optimization passes available (see PassManagerBuilder::populateModulePassManager in lib/Transforms/IPO/PassManagerBuilder.cpp to get an idea of what is available). It looks like the current pass manager used by llvmpipe is in create_pass_manager in src/gallium/auxiliary/gallivm/lp_bld_init.c and it adds only a few optimization passes.

To add autovectorization to llvmpipe, I think adding something like this after the call to LLVMAddGVNPass(gallivm->passmgr); will work:

#if HAVE_LLVM >= 0x301
LLVMAddBBVectorizePass(gallivm->passmgr);
/* BBVectorize depends on other passes for cleanup... */
LLVMAddInstructionCombiningPass(gallivm->passmgr);
LLVMAddEarlyCSEPass(gallivm->passmgr);
#endif

I've never really used the C API, and I'm not really sure how to pass tuning parameters through (and some tuning might be helpful or necessary here -- integration between the optimization passes and the backends is not as good yet as it should be), but this would be a start.

Thanks in advance,
Hal

P.S. Please feel free to forward or repost this message elsewhere if you feel that would be helpful or more appropriate.
I'm still out of the country on this nearly month-long business trip, but hopefully a few Phoronix readers would be interested in poking around with making these code changes as it could yield some interesting performance gains for this promising GPU fallback driver. LLVMpipe is now used as the fallback for Ubuntu and Fedora when no hardware GPU driver is available.

About The Author
Michael Larabel is the principal author of Phoronix.com and founded the web-site in 2004 with a focus on enriching the Linux hardware experience and being the largest web-site devoted to Linux hardware reviews, particularly for products relevant to Linux gamers and enthusiasts but also commonly reviewing servers/workstations and embedded Linux devices. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics hardware drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated testing software. He can be followed via and or contacted via .
Latest Linux Hardware Reviews
  1. Even With Re-Clocking, Nouveau Remains Behind NVIDIA's Proprietary Linux Driver
  2. The Power Consumption & Efficiency Of Open-Source GPU Drivers
  3. AMD R600g/RadeonSI Performance On Linux 3.16 With Mesa 10.3-devel
  4. Intel Pentium G3258 On Linux
Latest Linux Articles
  1. AMD Catalyst 14.6 Does Slightly Better With APITest OpenGL Tests
  2. Updated Source Engine Benchmarks On The Latest AMD/NVIDIA Linux Drivers
  3. Nouveau vs. Radeon vs. Intel Tests On Linux 3.16, Mesa 10.3-devel
  4. KVM Benchmarks On Ubuntu 14.10
Latest Linux News
  1. Builder: A New Development IDE Being Built For GNOME
  2. GDB 7.8 Betters Python Scripting, Adds Guile Support
  3. GNOME's GTK+ Is Still Striving For A Scene Graph, Canvas API
  4. Unreal Tournament Looks Great For Team Deathmatch
  5. LibreOffice 4.3 Released With Many Exciting Changes
  6. GNOME/GTK On Wayland Gains Focus At GUADEC
  7. GNOME Stakeholders Take Issue With Groupon Over their Gnome
  8. GStreamer VA-API Plug-In Update Adds New Features
  9. Qt 5.4 Going Into Feature Freeze Next Week With Exciting Changes
  10. OpenSUSE Factory Turns Into Rolling Release Distribution
Latest Forum Discussions
  1. Grand Theft Auto Running On Direct3D Natively On Linux Shows Gallium3D Potential
  2. Open-source drivers on ATI R7 260X
  3. AMD Athlon 5350 APU On Linux
  4. Debian + radeonsi
  5. Linus Torvalds On GCC 4.9: Pure & Utter Crap
  6. Updated and Optimized Ubuntu Free Graphics Drivers
  7. List of Linux friendly Kickstarter projects
  8. Porting Mesa to the Playstation 2