Intel's Haswell Architecture Analyzed: Building a New PC and a New Intel
by Anand Lal Shimpi on October 5, 2012 2:45 AM ESTTSX
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.
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Peanutsrevenge - Friday, October 5, 2012 - link
What the hell are you guys bitching about?Of course the iPhone articles are going to be longer and more numerous than GS3 articles.
iPhone releases come with new iOS releases and have their own eco-system.
Android phone releases use a common OS across them and therefore much of what's in one article doesn't need repeating in another.
Anand liking Apple is not our problem, I can see why people like them (not so much Anand) and that's fine, personally I dislike them (hate was originally typed, but was edited due to being incorrect), but still respect them and respect people who purchase their products (and pay for their litigation).
An entire page of comments talking about how Anand isn't allowed to like or talk about Apple products because you guys don't like is ridiculous, they're a PC company and should exist on a PC website.
Grow up.
Kepe - Friday, October 5, 2012 - link
Sure, but I'm talking about dedicating entire, long articles to such things as the iPhone display or why it doesn't have a certain feature and so on. The SGS III has a very interesting display, too. Still it didn't get nearly as much attention. Of course Anand is allowed to talk about Apple products. What I want, though, is Anand(tech) to be as thorough in reviewing other products, too, or then stop making those huge articles only about Apple products. Because that is biased.In the Macbook Pro Retina article Anand talked about the cooling system and the fan blades for one page. When I read any other laptop review on Anandtech, cooling is briefly described in a sentence or two.
Dedicating so much attention to just one company's products makes it look like Anandtech is biased. And that is not good.
Magik_Breezy - Sunday, October 14, 2012 - link
Hopefully because of these comments they'll finally see what we want, not some Apple crap. Good engineering stupid managementSpunjji - Thursday, October 18, 2012 - link
Nailed it.vFunct - Saturday, October 6, 2012 - link
Android products would get more coverage if they bothered to do any engineering on them. Since they don't push the technology the way Apple does, they don't need a more in-depth review.StevoLincolnite - Saturday, October 6, 2012 - link
You're kidding right? Hardware wise Apple has always been behind the curve compared to the competition in every facet of it's product line-ups or very quickly beaten.lmcd - Saturday, October 6, 2012 - link
Umm, I would disagree there. Apple has always been ahead of the curve in GPUs and this is the FIRST TIME SINCE BEFORE THE A-SERIES that Apple has had a GPU without an overwhelming lead on the competition for more than half a year.*While GPU selection isn't always huge, it's one of the biggest points of differentiation in mobile chips, along with power use.
*excluding the A4 if you count from when it was first in a phone as opposed to in a tablet.
Magik_Breezy - Sunday, October 14, 2012 - link
The last time I played a game on my phone was about 8 months ago and I'm 15! To say that Apple pushes their hardware is naive as it gets.The Galaxy S III was the best purchase Ive made, even my mum doesn't like my iPhone 4.
vFunct - Sunday, October 7, 2012 - link
Yes, Apple products are always ahead of compromised Android products.Android devices are badly engineered, like incorporating LTE when the battery can't handle it, for example. Apple doesn't compromise on their design.
Kepe - Monday, October 8, 2012 - link
How much does Apple pay you for a comment praising them?