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The Impact of Bulldozer's Pipeline

With a new branch prediction architecture and an unknown, but presumably significantly deeper pipline, I was eager to find out just how much of a burden AMD's quest for frequency had placed on Bulldozer. To do so I turned to the trusty N-Queens solver, now baked into the AIDA64 benchmark suite.

The N-Queens problem is simple. On an N x N chessboard, how do you place N queens so they cannot attack one another? Solving the problem is incredibly branch intensive, and as a result it serves as a great measure of the impact of a deeper pipeline.

The AIDA64 implementation of the N-Queens algorithm is heavily threaded, but I wanted to first get a look at single-core performance so I disabled all but a single integer/fp core on Bulldozer, as well as the competing processors. I also looked at constant frequency as well as turbo enabled speeds:

Single Core Branch Predictor Performance—AIDA64 Queens Benchmark

Unfortunately things don't look good. Even with turbo enabled, the 3.6GHz Bulldozer part needs another 25% higher frequency to equal a 3.6GHz Phenom II X4. Even a 3.3GHz Phenom II X6 does better here. Without being fully aware of the optimizations at work in AIDA64 I wouldn't put too much focus on Sandy Bridge's performance here, but Intel is widely known for focusing on branch prediction performance.

If we let the N-Queens benchmark scale to all available threads, the performance issues are easily masked by throwing more threads at the problem:

SMP Branch Predictor Performance—AIDA64 Queens Benchmark

However it is quite clear that for single or lightly threaded operations that are branch heavy, Bulldozer will be in for a fight.

Power Management and Real Turbo Core Cache and Memory Performance
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  • TekDemon - Wednesday, October 12, 2011 - link

    Yeah I paid $179 for my i5 2500K and it hums along at 4.8Ghz (can hit 5Ghz+ but I wanted to keep the voltages reasonable). Clock for clock bulldozer is slower since it's only competitive when the higher clocked part is compared to a stock 2500K. Reply
  • jleach1 - Friday, October 21, 2011 - link

    Their cores offer, what 75% the speed of a normal core?

    The fact is, this supposed "8" core processor performs worse than AMDs own 6 core processor. There's no way we can get away with calling it an 8 OR a 6 core.

    For all intents and purposes, it's a quad core.
    Reply
  • estarkey7 - Wednesday, October 12, 2011 - link

    You took the words right out of my mouth! I am a big AMD fanboy, and I was waiting with baited breath to jump on the bulldozer bandwagon for my next rig (and I probably still will). But this is ridiculous! I'm a computer engineer and where the hell were the simulations AMD? Seems like you could have halved the L3 and kept in the extra FP resources and been better than what you are doing now.

    Also, don't bitch about that Windows 7 doesn't realize the architecture of Bulldozer, you knew that 18 months ago, so you should have been writing a patch so that would have been a non issue.

    The absolutely, positively only reason i will by an 8150-FX is that my current desktop is a dual core Athlon running at 2.2GHz. So to me, the performance increase over my current desktop would be massive. But on second thought, if I have stuck with such a slow system this long, I might another 3-5 months for Piledriver.
    Reply
  • Taft12 - Wednesday, October 12, 2011 - link

    <i>The power consumption is absolutely through the roof -- unacceptable for 32nm, really!</i>

    Uhh, you did see the bar graph for idle power usage, right? And keep in mind this is an 8-core CPU compared to 4- and 6-core competitors.

    Like you, I'm also very interested in the 4- and 6-core Bulldozers. Anand let us down by only reviewing the flagship Llano. Hopefully he doesn't do the same with Bulldozer.
    Reply
  • Tom Womack - Wednesday, October 12, 2011 - link

    Yes, the idle power is significantly worse than either of the Sandy Bridge platforms he's comparing it to Reply
  • JasperJanssen - Wednesday, October 12, 2011 - link

    What Anand reviews is mostly down to what AMD will let him have -- even sites the size of Anandtech don't simply get to call and order parts from a catalogue for review samples. Reply
  • Taft12 - Wednesday, October 12, 2011 - link

    AMD doesn't have much control over "review samples" that can be purchased at retail, as you can do with the A4-3300 et al. for weeks now Reply
  • enterco - Wednesday, October 12, 2011 - link

    I read that 'at 1920x1200/1080 the gaming performance depends much mure on the GPU. Anyway, I'm happy with my i5-2500k ;-), Bulldozer does not seem to worth the wait. Reply
  • ninjaquick - Wednesday, October 12, 2011 - link

    Blame shitty game developers. Reply
  • AssBall - Wednesday, October 12, 2011 - link

    Kinda what I was thinking. When they are all developing games for a 6 year old 3 core PowerPC system with 512MB RAM (xbox) instead of a computer, its no bloody wonder. Reply

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