TSX

Johan did a great job explaining Haswell's Transactional Synchronization eXtensions (TSX), so I won't go into as much depth here. The basic premise is simple, although the implementation is quite complex.

It's easy to demand well threaded applications from software vendors, but actually implementing code that scales well across unlimited threads isn't easy. Parallelizing truly independent tasks is the low hanging fruit, but it's the tasks that all access the same data structure that can create problems. With multiple cores accessing the same data structure, running independent of one another, there's the risk of two different cores writing to the same part of the same structure. Only one set of data can be right, but dealing with this concurrent access problem can get hairy.

The simplest way to deal with it is simply to lock the entire data structure as soon as one core starts accessing it and only allow that one core write access until it's done. Other cores are given access to the data structure, but serially, not in parallel to avoid any data integrity issues.

This is by far the easiest way to deal with the problem of multiple threads accessing the same data structure, however it also prevents any performance scaling across multiple threads/cores. As focused as Intel is on increasing single threaded performance, a lot of die area goes wasted if applications don't scale well with more cores.

Software developers can instead choose to implement more fine grained locking of data structures, however doing so obviously increases the complexity of their code.

Haswell's TSX instructions allow the developer to shift much of the complexity of managing locks to the CPU. Using the new Hardware Lock Elision and its XAQUIRE/XRELEASE instructions, Haswell developers can mark a section of code for transactional execution. Haswell will then execute the code as if no hardware locks were in place and if it completes without issues the CPU will commit all writes to memory and enjoy the performance benefits. If two or more threads attempt to write to the same area in memory, the process is aborted and code re-executed traditionally with locks. The XAQUIRE/XRELEASE instructions decode to no-ops on earlier architectures so backwards compatibility isn't a problem.

Like most new instructions, it's going to take a while for Haswell's TSX to take off as we'll need to see significant adoption of Haswell platforms as well as developers embracing the new instructions. TSX does stand to show improvements in performance anywhere from client to server performance if implemented however, this is definitely one to watch for and be excited about.

Haswell also continues improvements in virtualization performance, including big decreases to guest/host transition times.

Decoupled L3 Cache Haswell's GPU
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  • 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

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