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Does PCIe 3.0 matter for today’s GPUs? We test with the Radeon HD 7970

Update 23/12: We updated our original article from yesterday with more background information and included LuxMark (OpenCL) for completeness. Doesn't change the conclusions though…

For months now, certain smaller motherboard manufacturers have been hyping up PCI Express 3.0 compatibility and benefits to ignorant users, even going to the point of bashing one another with libelous advertisements (lol hammer smash motherboards into bits). Since the latest Intel's Sandy Bridge-E processors and AMD's Radeon HD 7970 officially supports the new signalling standard, we put that to the test to see if it does improve things.

The following is rephrased and quoted from Wikipedia's PCI Express entry:

The much delayed PCIe 3.0 standard is supposed to bring signal transfer bitrates to 8GT/s (double that of PCIe 2.0) and a number of optimizations for enhanced signaling and data integrity, including transmitter and receiver equalization, PLL improvements, clock data recovery, and channel enhancements for currently supported topologies

Updated Notes:

  • Sandy Bridge-E/X79 does support PCIe 3.0, but it is not officially validated by PCI-SIG yet
  • We did use the latest 1004/1005 BIOS for the Rampage IV Extreme which has latest CPU Microcode and PCIe 3.0 fixes
  • We've now thrown in LuxMark (OpenCL transfer intensive benchmark) in the screenshots below, which still shows the same results (minicule difference).
  • For our upcoming Crossfire review, we will include [email protected] and Bitcoin benchmarks. If there are any other compute heavy benchmarks you would like to see, put them in the comments section below
  • An AMD rep got in touch with us – to verify the active PCIe signalling standard, simply run a PCI Configuration Space Viewer like R/W and look for the 0x88 offset. Values are 0x1 = 1.0 speed, 0x2 = 2.0 speed, 0x3 = 3.0, speed 0x0 = undefined

The BIOS on our favourite ASUS Rampage IV Extreme (X79) allowed us to select the PCIe signalling standard for our tests (Editor's note: yes we did use the latest 1004 bios which has the CPU Microcode and PCIe 3.0 fixes)


PCIe 3.0 Benchmarks:


PCIe 2.0 Benchmarks:


Our conclusions? Only a <1% miniscule benefit thanks to tighter clock timings and PLL improvements  – today's high end GPU like the HD7970 and GTX590 barely even saturate PCIe x8 lanes (4GT/s). Perhaps we might see a different story with decent solid state storage setups and CPU interconnects.

Lennard Seah
Why can't I have sharks with frickin' laser beams attached to their heads

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