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
POST A COMMENT

248 Comments

View All Comments

  • zwillx - Monday, January 21, 2013 - link

    Apple. Or are you joking. I personally hate Apple and have since the original iMac but their engineering is top notch when it comes to getting ideal performance from silicon to user. So.. guessing that's the reference. Reply
  • Silma - Monday, October 08, 2012 - link

    A fine read, technically very comprehensive, but still overly melodramatic.

    While it is true that it is crucial for Intel to step a foot in the byod market some things still hold true:
    - In value and profit the PC processor market is much bigger than the byod processor market and will stay so for years because PCs, especially business PCs won't disappear anytime soon.
    - Nobody can touch Intel in this market, it has been proved for decades. Not AMD at the height of its success, not mighty IBM, not Sun, nobody.
    - Contrary to what you say Intel has a definitive production advantage and there are very few fabs able to compete. Note that Apple is incapable of producing processors, it is dependent on external manufacturers.
    - What Apple does with its processor is interesting business wise for its iPods/Pads/Phones, but Apple doesn't have the research power Intel and others have in the chip space and I can't see how it will innovate better than Intel and other competitors.
    - Intel is aware of its shortcomings, is pushing tremendously in the right direction. A competitor that doesn't rest on its laurels is a mighty threat, ARM beware.
    - If Apple stops using Intel processors, it will of course wipe a few hundred millions of Intel's turnover but won't be anything remotely dangerous for Intel
    - It remains to be seen that Apple users will accept yet another platform change.
    - It remains to be seen that it would make sense business-wise for Apple
    - I am quite sure many phone companies will be open about renewed chip competition and not letting a single platform become too powerful.

    All in all it seems to me Intel is as dangerous as ever, executing very well in its core business and heading towards great things in the phone/pad space.
    Reply
  • johnsmith9875 - Thursday, October 11, 2012 - link

    Why couldn't they at least stick to LGA2011? Reply
  • defiler99 - Tuesday, October 16, 2012 - link

    One of the best articles on Anandtech in some time. This is great original tech industry reporting. Reply
  • Gc - Saturday, January 12, 2013 - link

    Congratulations, an intel cpu engineer wrote around 27 Dec 2012:

    "... Anandtech's latest Haswell preview is also excellent; missing some key puzzle pieces to complete the picture and answer some open questions or correct some details but otherwise great. ..."

    http://www.reddit.com/r/IAmA/comments/15iaet/iama_...
    Reply
  • xaml - Thursday, May 23, 2013 - link

    This was first posted here a few handfuls of pages back as a comment by user "telephone". ^^ Reply
  • yhselp - Friday, March 29, 2013 - link

    A few questions.

    Is there going to be a replacement (37W) for the current IVB 35W quad-core part? Quite a few designs are now dependable on this, lower power quad-core option - Sony S-series and Razer Blade, to name a few.

    When can we expect all mobile CPUs (except maybe for the extreme series) to fall into the 10W-20W range? In three years' time and 10nm?

    The decision to not include GT3 with desktop parts is very disappointing. A 35/45W low-voltage part with GT3 would make for an excellent HTPC build, among other things. Is there a chance Intel change their mind and start shipping GT3 desktop parts at some point?
    Reply
  • JVimes - Tuesday, August 19, 2014 - link

    Does EU stand for Execution Unit? That was surprisingly hard to google for. Reply

Log in

Don't have an account? Sign up now