AMD Phenom In-Depth Performance Scaling Analysis

Overclocking/ by massman @ 2008-12-30

With the upcoming release of the Phenom II we take a look at what we can expect by overclocking every aspect of our Phenom X4 9950 CPU. HT Link, Memory, Northbridge and RAW CPU speed scaling is compared in-depth to help you get the most out of your Phenom setup.

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Memory frequency performance scaling

Memory frequency performance scaling:

These days there are two different types of common desktop platforms: the ones using a cpu with Integrated Memory Controller, such as AMD's Athlon64/Phenom and Intel's Core I7, and the ones with the memory controller inside the Northbridge. For the non-tech minded people under us, this may not seem to be that important -memory is still memory- but if you have a closer look at it, it actually does matter. Using an IMC has many advantages, the most important one being higher bandwidth and lower latencies, which will be translated into higher performance. And that's not so strange: the data lanes between memory and cpu, which serve as communication ports, are much shorter than those in an non-IMC platform. An example:

  • AMD Phenom <=> DDR2
  • Intel C2D <=> P45 <=> DDR2

    In the first example, the latency is only bottlenecked by the length of the lane between cpu and memory, whereas in the second example, the latency is bottlenecked by both lane between cpu and Northbridge and Northbridge and memory.

    Test settings:
  • Core frequency: 2800MHz
  • HTT frequency: 200MHz
  • HT Link frequency: 2000MHz
  • Northbridge frequency: 2000MHz
  • Memory timings: 4-4-4-10 2T Ganged(*)

  • Memory frequency: 200, 266, 333, 400 and 533MHz

    (Click for bigger version)

    Although we're happy to see that the memory frequency clearly has its effect in the theoretical memory benchmarks, we had hoped it would scale better in the more real world benchmark applications. The difference between 200MHz and 533MHz is there, yes, but will only make a big difference if your application is memory-hungry. Is this similar to the difference we will see when comparing AM2+ to AM3 platforms, which basically is only a difference between DDR2 and DDR3, which in itself is only a difference in memory frequency? We hope not!

    (*):Due to the design of the K10 processor, it's impossible to use memory timings below 4-5-5-X using the 533 divider. We used 4-5-5-16 in the comparison.

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    Comment from Kougar @ 2009/01/08
    Thought this was a great article...

    Just going to point out that while Phenom II increases performance, Phenom II decreased Uncore clocks from 2GHz to 1.8GHz. So AMD will be gaining that performance back with AM3 DDR3 processors launching soon, which will use a 2GHz Uncore.
    Comment from Massman @ 2009/01/08
    I'm looking quite forward to my PhII sample to compare the performance scaling.

    There's more to tell about the techy aspects of the P2 than one would think. Lostcircuits has some good insights: d=1