So, the front end hasn’t been profoundly overhauled; neither has the back end. It has exactly the same execution units as the most recent Core processors, but here again the engineers have worked on using them more efficiently.
With Nehalem, Hyper-Threading makes its great comeback. Introduced with the Northwood version of Intel’s NetBurst architecture, Hyper-Threading—also known outside the world of Intel as Simultaneous Multi-Threading (SMT)—is a means of exploiting thread parallelism to improve the use of a core’s execution units, making the core appear to be two cores at the application level.
In order to use parallel threads, certain resources—such as registers—must be duplicated. Other resources are shared by the two threads, and that includes all the out-of-order execution logic (the instruction reorder buffer, the execution units, and cache memory). A simple observation led to the introduction of SMT: the “wider” (meaning more execution units) and “deeper” (meaning more pipeline stages) processors become, the harder it is to extract enough parallelism to use all the execution units at each cycle. Where the Pentium 4 was very deep, with a pipeline having more than 20 stages, Nehalem is very wide. It has six execution units capable of executing three memory operations and three calculation operations. If the execution engine can’t find sufficient parallelism of instructions to take advantage of them all, “bubbles”—lost cycles—occur in the pipeline.
To remedy that situation, SMT looks for instruction parallelism in two threads instead of just one, with the goal of leaving as few units unused as possible. This approach can be extremely effective when the two threads are executing tasks that are highly separate. On the other hand, two threads involving intensive calculation, for example, will only increase the pressure on the same calculating units, putting them in competition with each other for access to the cache. It goes without saying that SMT is of no interest in this type of situation, and can even negatively impact performance.


I regard being late as a quality seal really. No point being first, if your info is only as credible as stuff on inquirer. Better be last, but be sure what you write is correct.
Perhaps, if you count being translated from French.
Nice article, good depth, well written
I don't know french, so no idea if it actually works. But I've tried from english to germany and danish, and viseversa. Also tried from danish to german, and the result is always the same - it's incomplete, and anything that is slighty technical in nature won't be translated properly. In short - want it done right, do it yourself.
You claimed the article on toms was a copy paste from another article. He merely stated that the article here was based on a french version.
I actually read the whole thing.
I just don't get TLP when RAM is cheap and the Nehalem/Vista can address 128gigs. Anyway, things have changed a lot since running Win NT with 16megs RAM and constant memory swapping.
1) How's the loop detection feature know when it is a loop ? The diagrams posted don't show any connection between it and the 'front' of the pipeline, so how can it know that the next operation is the same if it hasn't yet entered the loop?
2) On page 8 there's a diagram with a 4 socket setup showing 2 io hubs. Are they connected to the same pcie bus and whatever else they interface with? or are only 2 of the sockets able to directly access a given resource?
3) With the modular design, would one risk buying a cpu that doesn't work in a motherboard because it is intended for a 2 or 4 socket system? or are they all the same, simply with some qpi's disabled?
4) Am I right assuming that qpi replaces fsb when it has to communicate with an i/o hub only? (as shown in one of the top diagrams on page 8) Or is it used for every one of the 'blue' lines on the lower diagram (10 total in a 4 socket layout). The latter would mean 4 qpi's are barely enough to satisfy bandwidth needs in a server enviroment. I imagine an esx server with 4 processors (32 threads) can easily demand memory from dram pools not linked to the local core the threads are running on, and use 96GB/s (3x32) of the 102GB/s (4x12,8x2) total theoretical bandwidth in addition to some of the local 32GB/s bandwidth from the socket a given core/thread is running on. So if this scenario is correct, is it possible to increase the speed of the qpi (read: oc the link) to increase available bandwidth? And what happends if one would successfully find ddr3-1600 modules that would run within the 1,65v limitation? Wouldn't that mean the qpi was already at its limit? (38,4GB/s per dram pool x 3 sockets not local to the core that runs a thread). I know memory isn't truely the bottleneck in modern computers, but I still find it wierd that they put so much effort into the memory controller if it isn't actually the problem. Simply adding a few qpi links between the sockets and the chipset would've solved the bandwidth issue without limiting usable memory types by choosing a certain cpu. Sure it wouldn't have improved latencies, but honestly, who cares? neither in a gaming pc, netbook or any number of common server configurations is it the memory lantecy that is the bottleneck.
5) How much time should one assume is wasted when a core on conroe flushes the l2 cache? they seem to have solved the issue and as consequence increased cache latency (which should turn into slower overall cache performance). In english : can we expect any gain from this change?
6) Would the immensely increased tlb size improve performance in newer games which precache loads of data? (thinking quicker retrieval of texture data etc)
7) Page 12 mentions unalligned memory access, which I've never heard of before. Appearently compilers already try to avoid this situation, so can we expect the improvement to handling such to be of interest? What's the point of improving a feature to handle a situation that hardly ever arises in the first place?
http://www.xbitlabs.com/articles/cpu/display/replay.html
This was a very good article and is not a copy ... well done Fedy !!
perhaps it will burn out the IMC within the chip since its all done at 45nm, 1.6+v would be deadly, imagine air cooling a 3ghz quad core chip at ~2v? i take it it shares the rail even within the cpu so
depends on how connected that ram is, there might be advantages etc this way, and it also makes you wonder if AMD suffers from this - iv heard of extreme overclockers killing ram channels on AMD's etc
on the other hand who cares about high performance memory - 3 x 1333mhz is going to be better then 2 x 1600+mhz channels etc, along with the fact its an IMC based setup etc and average maximum bandwidths of ~32gb/s vs the current average maximum of ~12.8gb/s etc
as for the memory issue. Who'd want to run 3x1333 if they could run 6x1600 ? any enthusiast will only be satisfied with the best, and 1333 just isn't it. Not even 1600 is. ddr3-1333 is basicly obsolete, and it's not even mainstream yet. It's a disaster really.
A case of perhaps minimising reflected impedence?
Just my theory anyway ... remember ... I am only here for the humour ... not the technology.
AMD4LIFE