Originally Posted by Blameless
Bulldozer doesn't have hyperthreading or any form of simultaneous multithreading. It has eight cores, grouped into tightly bound pairs.
I'll say it again:
Point out anything that makes a BD core not a core and I will show you a chip before it that shared, or was missing, the same feature and is near universally regarded as full core/CPU.
AMD's official line on Bulldozer is that it's a "third way" between traditional multicore and simultaneous multithreading (SMT). In the former type of design (also called chip multiprocessing, or CMP), each concurrently running thread runs on a separate core; contrast this to SMT, where two or more threads can share the same core by executing simultaneously.
AMD pitches Bulldozer as a middle ground between these two approaches, where two threads share a single front-end but have separate integer execution resources.
After looking closely at Bulldozer, it's best described as a new form of SMT—AMD's "third way" description isn't inaccurate, but it's most useful to think of Bulldozer as an approach to SMT that builds on what has come before.
This is about a presentation given by AMD at HotChips 2010. It's almost completely about SMT(HyperThreading) vs Bulldozer.
So, if SMT (or “core sharing”) yields both positive and negative results, what is the better answer? How about more cores? When you add more cores, you add more throughput. Period.
When you run multiple threads over multiple cores, you can expect better performance, and that is the AMD strategy. With “Magny Cours” we’re planning 8 and 12 cores per processor running 8 and 12 threads, not 8 or 12 threads sharing 4 or 6 cores. No sharing needed, every thread can be as selfish as it needs to be. Then in 2011, we plan to introduce “Interlagos” and increase the core count again, to 12 and 16. With “Interlagos” we’re designing some shared components that help reduce power consumption and die size, but you won’t see us sharing integer pipelines, the “meat” of the core.
By keeping discrete integer cores, and delivering more of those cores per CPU, AMD is designing processors that are designed to help you get more throughput for your enterprise applications.
While not about Bulldozer specifically, it does reinforce their view of adding more integer cores as a better alternative to SMT.
I will, however, add that I agree that Bulldozer is technically an eight-core CPU. Core obviously referring to Integer Cores since there is nothing else called a "core" in a processor. However it's clear that the design choice of Bulldozer was at least partly trying to compete w/ Intel's HyperThreading.