Nehalem - Everything You Need to Know about Intel's New Architecture
by Anand Lal Shimpi on November 3, 2008 1:00 PM EST- Posted in
- CPUs
Understanding Nehalem’s Server Focus (and Branch Predictors)
I’ve talked about these improvements before so I won’t go into such great detail here, but Nehalem made some moderate improvements on Intel’s already very strong branch predictors.
The processor now has a second level branch predictor that is slower, but looks at a much larger history of branches and whether or not they were taken. The inclusion of the L2 branch predictor enables applications with very large code sizes (Intel gave the example of database applications), to enjoy improved branch prediction accuracy.
The renamed return stack buffer is also a very important enhancement to Nehalem. Mispredicts in the pipeline can result in incorrect data being populated into Penryn's return stack (a data structure that keeps track of where in memory the CPU should begin executing after working on a function). A return stack with renaming support prevents corruption in the stack, so as long as the calls/returns are properly paired you'll always get the right data out of Nehalem's stack even in the event of a mispredict.
The targeted applications here are very important: Nehalem is designed to fix Intel’s remaining shortcomings in the server space. Our own Johan de Gelas has been talking about Intel not being as competitive in the server market as on the desktop for quite some time now. He even published a very telling article on Nehalem’s server focus before IDF started. While many of Nehalem’s improvements directly impact the desktop market, motivating its design were servers.
This is an important thing to realize because this whole architecture, where Nehalem and its predecessors came from started on the mobile side of the business with Banias/Pentium-M and Centrino. We may have just come full circle with Nehalem, where we once again have the server market driving the microprocessor design for the desktop and mobile chips as well.
The key distinction here and what will hopefully prevent Nehalem’s successors from turning into Pentium 4 redux is Intel’s performance/power ratio golden rule. Nehalem and Atom were both designed, for the first time ever in Intel history, with one major rule on power/performance. For every feature proposed for Nehalem (and Atom), for each 1% increase in power consumption that feature needed to provide a corresponding 2% or greater increase in performance. If the feature couldn’t equal or beat this ratio, it wasn’t added, regardless of how desirable.
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qurious69ss - Friday, August 22, 2008 - link
You sound like one of those sad fanboys from amdzone. Tell dimentia to get a life.X1REME - Friday, August 22, 2008 - link
wow, this whole cpu is a copy of a amd cpu and you expect amd fan boys to not get amd with you, secondly this fantasy is baseless until you can compare it to an offering from the AMD team (Shanghai & Deneb). AMD is still KING with there OPTERON and most likely will be in the future with there new cpu coming soon for the server and also for the desktop.DigitalFreak - Friday, August 22, 2008 - link
Learn to spell, you goober.X1REME - Friday, August 22, 2008 - link
OK DORK, am sure you have never made a mistake (there=their) Duh. I bet your some kid all hyped up for the i7 who wishes Xmas comes early lol. Anyway it’s not a desktop chip, it’s a sever chip DUH. It’s meant to compete with the AMD Opteron chip (the best). Although Opteron will lose its crown, it won’t be to i7 but to Shanghai (AMD new latest and greatest). And like I said b4, Deneb will clear anything up out of place.The reason amd does not grab a microphone and star shouting at the top of their voice is because amd doesn't have the resources and money in comparison with Intel. If it reveals too much about its future strategy and Intel likes that strategy (like the Opteron, HT, On-board mem etc) there is a big theoretical chance that Intel could take this idea and deliver a product well before AMD. So it’s not over until amd says its.
snakeoil - Thursday, August 21, 2008 - link
nehalem fails,it was supposed to be superior to core 2, intel was against the wall this time, why?, because, the old front bus architecture was lagging more more in the server arena and becoming a bottleneck ,compared to hypertransport, so intel is forced to abandon the front side bus, but the strong point of core 2 is that because you don't have and integrated memory controller you can stuff the processor with a huge L2 cache.so, nehalem sucks in gaming,there is no way that the enthusiast is going to pay more for a processor that produce less fps that they actually have.
and the hyperthreading is a risky move, hypertrheading is known por being power hungry, and although produce gains in some applications,some servers applications actually runs slower, so in many cases the old hyperthreading had to be disabled.
nehalem is crippled for the enthusiast,and the regular user.
nuff said.
AssBall - Saturday, August 23, 2008 - link
You musta missed where Anand says several times its not intended for better gaming? It will be significantly faster than Penryn for multithreaded applications. I guess I don't see how this makes it "fail". Maybe in your fantasy world where 90% of the CPU market are "enthusiasts".snakeoil - Saturday, August 23, 2008 - link
enthusiasts drive the market you fruityassUnlimitedInternets36 - Saturday, August 23, 2008 - link
LOL this year Satan err Santa is going to take away your PC because you don't deserve to have one anymore You Jaded nerd.Gasaraki88 - Friday, August 22, 2008 - link
Thanks! I never knew there was a expert on CPU design in the house. I've learn so much from your well researched, tested and thought out comment...pool1892 - Friday, August 22, 2008 - link
first of all the enthusiast market is a very tiny niche, it would not kill intel if you were right.but you are not. the L2 of penryn (and banias) is much more like the nehalem L3 than the nehalem L2. and if you have a single threaded game it now has 8mb at similar latencies, but with a second buffer, the 256k L2, and a MUCH smaller cache miss penalty.
concerning hyperthreading: please read the article first. nehalem switches off what it does not need, powerwise. and about fiftytwo other very vaild arguments.