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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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  • Iketh - Wednesday, October 12, 2011 - link

    AMD Exec a year ago: "We about ready to release BD?"

    AMD Engineer: "Soon. At 4ghz, we're actually slower per thread and using double the power than Phenom at 3.4ghz, but we'll get there..."

    AMD Exec: /gquit
    Reply
  • lyeoh - Wednesday, October 12, 2011 - link

    Bulldozer reminds me of the P4/Prescott for some reason ;).

    High clock, high watts, but not enough performance.

    Might be faster in parallelizable tasks but most people with such tasks would just buy more computers and build large clusters.
    Reply
  • Iketh - Wednesday, October 12, 2011 - link

    The processors are popping up on Newegg now... the 8120 for $220 and 6100 for $190 Reply
  • vol7ron - Wednesday, October 12, 2011 - link

    Sigh... I made the mistake in buying a Prescott. Not to mention I bought an "E" batch, which ran even hotter and weren't as overclockable. Reply
  • actionjksn - Wednesday, October 12, 2011 - link

    Yeah I had one of those hot potato's too. Back then we thought Intel was finished. Reply
  • just4U - Thursday, October 13, 2011 - link

    ckryan, you stated you were blown away by the 2500K yes? It's odd you know.. I've owned a PII 920, PII 1055, PII 955 (tested lots of lowbie $60-80 parts from AMD to) .. also used a i7 920, i7 955 i5 2500k i7 2600k (my most recent one) and .. I am not blown away by any of them..

    Last time I was blown away by a cpu was the Q6600..(before that the A64 3200+) since then other cpu's have been better but not so much so that I'd say that it was night and day differences.
    Reply
  • CeriseCogburn - Wednesday, March 21, 2012 - link

    Ok that was some enormously skilled twisting and spinning. BD is an epic failure, period. I can't envision anyone with any needs, need, or combo thereof choosing it.\
    It's so bad amd lied about it's transistor count.
    Forget it, it's an epic fail and never anything more.
    Reply
  • jiffylube1024 - Wednesday, October 12, 2011 - link

    Ugh, BD is quite the disappointment. The power consumption is absolutely through the roof -- unacceptable for 32nm, really!

    With that said, I am very intrigued in the FX-4100 4-core 3.6GHz part. This should be the replacement for the Athlon II 2-4 core series, and I'm very interested to see how it does vs ~3 GHz Athlon II X2's, X3's and X4's.
    Reply
  • yankeeDDL - Wednesday, October 12, 2011 - link

    Wow ...
    I'm blown away.
    I have been waiting for BD's reviews and benchmarks for months. I have waited for BD for my new rig.
    I have used AMD for the past 8 years and I am ... was convinced that it always offered, by far, the best price/performance ratio for entry-level, mid range PCs.
    I am a still a big fan of AMD ... but I have to stand corrected. BD is a POS. Longer pipelines? Didn't they learn anything from Pentium 3/4 debacle?
    A Phenom II X6 is almost always better than BD, even in power consumption. Come on: if BD had come out shortly after the Phenom I could see it as an incremental improvement, a new baseline to build upon. But it took AMD years to come out with BD ... and this is the result? Disappointing.
    I mean, betting everything on higher clock frequencies? At 4GHz? It's no wonder that Intel's IPC improvements are crunching BD: IPC is all about doing more with the same power, clock speed is all about throwing more power to do the same faster ...
    Boy. This ruined my day.
    Reply
  • yankeeDDL - Wednesday, October 12, 2011 - link

    By the way, no matter how AMD slices it, I see the FX-8* as a 4-core CPU. A glorified ohene, but still a 4-core.
    If I was AMD, I would have considered a fair goal to obliterate the i5-2500 performance with the new FX-8 family, instead it comes short most of the times.
    What were they thinking?
    Reply

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