Multi-GPU Setups: The Basics Of CrossFire And SLI

CPU Scaling On AMD

How much CPU performance do you really need to adequately utilize a current-generation AMD graphics card? Since this is a CrossFire test, the CPU must be powerful enough to keep both Radeon HD 5850 GPUs maxed out simultaneously.

In order to measure how CrossFire performance scales with CPU performance, we overclocked the Core i5 CPU from 2.66 GHz to 3.99 GHz in eight steps. Past experience with CrossFire would suggest that a bit of extra CPU performance surely can't hurt if you want to squeeze out those extra frames per second. However, modern high-resolution gaming with lots of anti-aliasing puts most of the load on the graphics cards.

Increasing CPU performance hardly seems to have any effect at all when using the newest 3D engines. Only the slightly older DirectX 9 Source engine (Half Life 2, Left 4 Dead, Left 4 Dead 2) shows meaningful differences.

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  • Redsnake77
    Good article. Totally agree with difference in ease of setup having gone from a pair 8800GTX OC2's in SLI to 5850's in crossfire, I miss my 8800GTX monsters they were great cards. Also agree about processor speed. I'd noticed in a few games (some are more noticeable than others) the framerate would slowly decrease then spring back up again, it was bugging me hugely. It was most noticeable in Dirt and Grid, two games I hadn't played since my old E6850 with the 8800's. Ran a fraps benchmark and you could see it cyclicly droping down through numbers 120, 118, 114, 110, down to 94fps, then jumping back upto 120+ and decreasing again. I ran Core Temp and straight away I could see the multiplier starting at 16 then dropping increntally down to 12 then jumping back up to 16. So I kept the voltages all stock and increased the baseclock to 160MHz, Loaded up the game, the multiplier now stays at 12, but the framerate is stable at 120-124fps with a processor speed of just under 2GHz. But at stock clocks why wouldn't the multiplier not just stay at 16?
  • Redsnake77
    This is on an i7 930, GA-EX58-UD5, 6GB 1600MHz DDR3, 2 Sapphire 5850 Toxic GPUs, and Win 7 64bit.
  • nesters
    ATI doesn't have terrible drivers, nVidia does.

    Well, ATI has some problems with Crossfire but remember that you can mix up different cards but with SLI you can only use the same card from same manufacturer. This might explain why drivers fail with Crossfire setup.
  • redkachina
    cmon what's with all these spam?..
  • Redsnake77
    I know, it's getting stupid, and the mods don't seem to be doing anything about it.