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

Bettering Radeon Gallium3D Performance With PCI-E 2.0

Michael Larabel

Published on 20 January 2012
Written by Michael Larabel
Page 1 of 4 - 59 Comments

While it will not take you up to the speeds of the Catalyst driver, besides the 2D color tiling patches, there are a few other outstanding features not yet enabled-by-default in the open-source Radeon graphics driver that can yield some performance boosts. One of these other features is enabling PCI Express 2.0 support within the Radeon DRM.

While the PCI Express 2.0 specification has been out since early 2007, been supported by Intel motherboards since 2007 with the X37 chipset, and has been supported by ATI graphics cards going back to the Radeon HD 3000 series, "PCI-E Gen2" support isn't yet enabled by default within the Radeon DRM. PCI Express 2.0 doubles the transfer rate of PCI Express 2.0 and the per-lane throughput is doubled to 500MB/s, among other improvements to the specification. With the Radeon HD 7000 "Southern Islands" series, AMD graphics cards are now up to supporting PCI Express 3.0.

Taking full advantage of PCI Express 2.0 for Radeon graphics cards involves setting a few registers related to the PCI-E link width and speed control. The code has been there for the supported generations of Radeon hardware for many months now, but it is not on by default. Like the Intel RC6 and Active State Power Management problems in the Linux kernel, PCI-E Gen2 is not on by default at this time due to a few hardware-specific problems. For some problematic systems, having the Radeon DRM with PCI Express 2.0 support enabled will cause a corrupted screen upon mode-setting. The problem comes down to compatibility issues with some motherboards. For over a year now the PCI-E Gen2 support has been concealed behind a kernel module parameter.

Those wishing to take advantage of PCI Express 2.0 with supported motherboards (nearly all Intel and AMD motherboards from 2008 and newer) and graphics cards (Radeon HD 3000 series and newer) must boot the kernel with the "radeon.pcie_gen2=1" on the kernel command line (or probe the radeon DRM with "pcie_gen2=1"), otherwise the graphics card will still be operating at PCI Express 1.0 speeds. Even with the forthcoming Linux 3.3 kernel, PCI-E 2.0 support is still off by default with the Radeon driver.

Across all of the motherboards and graphics cards I've tested, PCI Express 2.0 support has operated without fault -- for this latest round of testing and going back months. For many OpenGL workloads, running the graphics card with PCI-E 2.0 transfer rates does result in noticeable performance improvements.

To illustrate the performance benefits of booting with "radeon.pcie_gen2=1", here are some new benchmarks with and without this option. The system was from the Intel Core i7-3960X setup while using the Linux 3.2 kernel, Mesa 8.0-devel Git, the latest xf86-video-ati DDX, and an otherwise stock Ubuntu 11.10 host. The graphics cards tested were an ATI Radeon HD 4670, ATI Radeon HD 4770, ATI Radeon HD 4890, ATI Radeon HD 5450, ATI Radeon HD 5750, AMD Radeon HD 6870, and AMD Radeon HD 6950. Swap buffers wait was disabled during testing.

Latest Articles & Reviews
  1. OS X 10.10 vs. Ubuntu 15.04 vs. Fedora 21 Tests: Linux Sweeps The Board
  2. The New Place Where Linux Code Is Constantly Being Benchmarked
  3. 18-GPU NVIDIA/AMD Linux Comparison Of BioShock: Infinite
  4. Phoronix Test Suite 5.6 Adds New Phoromatic Enterprise Benchmarking Features
  5. OpenGL Threaded Optimizations Responsible For NVIDIA's Faster Performance?
  6. Big Graphics Card Comparison Of Metro Redux Games On Linux
Latest Linux News
  1. Git 2.4.0-rc0 Does A Ton Of Polishing
  2. The Most Common, Annoying Issue When Benchmarking Ubuntu On Many Systems
  3. Mesa Is At Nearly 1,500 Commits This Year
  4. Gestures & Other GTK3 Features For LibreOffice
  5. It's Now Easier To Try PHP 7 On Fedora & RHEL
  6. BQ Is Cleaning Up Their Aquaris E4.5 Ubuntu Kernel
  7. Allwinner Continues Jerking Around The Open-Source Community
  8. NVIDIA Linux 349.12 Beta Has Improved G-SYNC & VDPAU Features
  9. Canonical Just Made It Even Easier To Benchmark Ubuntu Linux In The Cloud
  10. NVIDIA GeForce GTX TITAN X Linux Testing Time
Most Viewed News This Week
  1. Introducing The Library Operating System For Linux
  2. AMD Is Hiring Two More Open-Source Linux GPU Driver Developers
  3. New SecureBoot Concerns Arise With Windows 10
  4. GNOME Shell & Mutter 3.16.0 Released
  5. GNU Nano 2.4.0 Brings Complete Undo System, Linter Support & More
  6. Systemd Change Allows For Stateless Systems With Tmpfs
  7. GCC 5 Compiler Is Getting Close To Being Released
  8. Chromebooks Powered By The MIPS Pistachio, Linux Support Evolving