Prioritizing ILP

Intel has held the single threaded performance crown for years now, but the why is really quite easy to understand: it has prioritized extracting instruction level parallelism with every generation. Couple that with the fact that every two years we see a "new" microprocessor architecture from Intel and there's a recipe for some good old evolutionary gains. The table below shows the increase in size of some major data structures inside Intel's architectures for every tock since Conroe:

Intel Core Architecture Buffer Sizes
  Conroe Nehalem Sandy Bridge Haswell
Out-of-order Window 96 128 168 192
In-flight Loads 32 48 64 72
In-flight Stores 20 32 36 42
Scheduler Entries 32 36 54 60
Integer Register File N/A N/A 160 168
FP Register File N/A N/A 144 168
Allocation Queue ? 28/thread 28/thread 56

Increasing the OoO window allows the execution units to extract more parallelism and thus improve single threaded performance. Each generation Intel is simply dedicating additional transistors to increasing these structures and thus better feeding the beast.

This isn't rocket science, but it is enabled by Intel's clockwork fab execution. Designers can count on another 30% die area to work with every 2 years, so every 2 years they increase the size of these structures without worrying about ballooning the die. The beauty of evolutionary improvements like this is that when viewed over the long term they look downright revolutionary. Comparing Haswell to Conroe, the OoO scheduling window has grown by a factor of 2x, despite generation to generation gains of only 14 - 33%.

The Haswell Front End Haswell's Wide Execution Engine
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  • CaptainDoug - Friday, October 05, 2012 - link

    Quite the read. Very informational. Anandtech has some of the best tech writers. True online journalism. Sometimes i miss that while reading tech blogs... You guys are a cut above.. at least one. Reply
  • colonelclaw - Friday, October 05, 2012 - link

    Couldn't agree more, this article really brightened up what was otherwise a pretty miserable afternoon here in London.

    When am I going to be able to walk into a shop and buy something with Haswell inside it? Next March maybe?
    Reply
  • Kepe - Friday, October 05, 2012 - link

    As stated in the article, Haswell is coming in the summer of 2013. Reply
  • linuxlowdown - Saturday, October 06, 2012 - link

    Tag team Intel fanboy puke. Reply
  • Azethoth - Sunday, October 07, 2012 - link

    How do I downvote stupid crap like this "Tag team Intel fanboy puke." comment so that collectively we can see high quality comments without having to wade through the interturds as well? It really takes away from the best article I have read in a long time. Not because it is about Intel, but because it is about the state of the art. Reply
  • medi01 - Tuesday, October 09, 2012 - link

    Well, I'd also ask how do I downvote stupid butt kissing like OP, while we are at rating.... Reply
  • Kisper - Saturday, October 20, 2012 - link

    Many people enjoy well written and informative articles. Are you telling me that if you wrote, you would not enjoy positive feedback from your readers? Reply
  • CaptainDoug - Tuesday, October 23, 2012 - link

    Exactly. Reply
  • actionjksn - Sunday, October 07, 2012 - link

    Why are you even on this article dumb fuck? I'm sure there is something that is of interest to you on the internet somewhere. Reply
  • medi01 - Tuesday, October 09, 2012 - link

    Not sure about him, but I've looked into this article to figure power targets for haswell (especially interesting to compare to ARM crowd), NOT to read orgasmic comments about eternal wizdom of Intel's engineering... Reply

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