AMD Bulldozer Official Information
This information is taken from few posts i saw in amd blogs http://blogs.amd.com , some questions from users and some answers from AMD.
Here is some important information.
AMD:
Each integer core will be able to run one software thread, and these threads can all be done simultaneously, unlike an SMT-type technology that lets two threads share one core. You typically find SMT technology on processors with much lower core counts, and its shared nature can create bottlenecks, even resulting in negative throughput in some cases.
As for core counts, here is what we have committed to at this point:
- “Interlagos” – 16-core server processor
- “Valencia” – 8-core server processor
- “Zambezi” – 8-core client processor
Users:
“The x86 core (Bobcat) of AMD Fusion APU Ontario will be based on Bulldozer architecture?” – Fabio Mendes
AMD:
Actually, these are different designs. The upcoming “Ontario” processor will be based on the “Bobcat” core, which has a different core architecture than “Bulldozer.” There have been some that have made the assumption that a Bobcat was just a scaled down “Bulldozer”, but they are, in fact, different. I’m sure that between the two there are similarities and some small sub-components that are shared, but you won’t see the modular design of “Bulldozer” in “Bobcat.”
Users:
“Will Bulldozer get a Turbo CORE for single threaded applications, just like the Thuban?” – Björn
AMD:
Yes. There will be a Turbo CORE feature for “Bulldozer”, but there will be some improvements from what you see in “Thuban” (our 6-core AMD Phenom™ processor). There are some enhancements to give it more “turbo”. This will be the first introduction of the Turbo CORE technology in the server processors. We expect that this will translate into a big boost in performance when using single threaded applications, and there should be some interesting capabilities for heavier workloads as well. We’re pretty excited about how this will be implemented with “Bulldozer”, but the specifics of how this is implemented and the expected performance gains will not be disclosed until launch.
Users:
“How much extra performance will we see when running two-threaded applications on one Bulldozer Module compared to two cores in different modules?” – Simon
AMD:
Without getting too specific around actual scaling across cores on the processor, let me share with you what was in the Hot Chips presentation. Compared to CMP (chip multiprocessing – which is, in simplistic terms building a multicore chip with each core having its own dedicated resources) two integer cores in a Bulldozer module would deliver roughly 80% of the throughput. But, because they have shared resources, they deliver that throughput at low power and low cost. Using CMP has some drawbacks, including more heat and more die space. The heat can limit performance in addition to consuming more power. Ask yourself, would you rather have a 4-cylinder engine that delivered 300HP or a 6-cylinder engine that delivered 360HP and consumed less gas? The cylinder to horsepower ratio for 4-cylinder is obviously higher (75HP/cylinder vs. the V6’s 60HP/cylinder), meaning that each cylinder can give you more performance. However, looking at the overall enginge, you are getting less total output; and you are getting that lower output at a higher cost (higher gas consumption).
Users:
“Current and forthcoming Nehalem EX based servers from IBM and HP top out at 8 sockets and 64 cores. What kind of vertical scalability can we expect from Bulldozer-based servers?” – David Roff
AMD:
Bulldozer will fit into the current “Maranello” and “San Marino/Adelaide” platforms. “Maranello” is our high performance platform that will support up to 4 CPUs. Combining a “Maranello” platform with the upcoming 16-core “Interlagos” processors, the total core density of a 4P system will reach as many as 64 cores.
The 8P x86 market today is pretty small. According to IDC, last year it accounted for roughly 7,915 total servers, down 26% from the year before (Source: IDC Quarterly Server Tracker, Q4 2009). If you want to say that 2009 was a bad year, from 2007 to 2008 the 8P x86 market was essentially flat as well, so that isn’t a growth engine. Part of what is impacting that market is the core and memory densities of today’s systems. People bought 8P servers to get to 48 cores (8 x 6-core) or to get to large memory footprints. Today’s 4P systems are meeting those needs at a lower price, with lower power consumption and lower latency. When we get to 2011 with “Bulldozer,” you’ll see an increase up to 64 cores, and we expect the total memory footprint will increase again.
The bottom line is, you’ll get the 64 cores that you want, you’ll just have to spend a lot less to get them; is that OK?
Users:
“Can you explain how is your Multi-threading technology different from Intels? What are the advantages?” - Vygantas
AMD:
We use actual, physical cores to handle multiple threads. Intel does this too, but they use HyperThreading technology to execute two threads on a single core as well which can create bottlenecks.
The challenge with HT is that it exploits gaps in the execution pipeline in order to get that second thread running. In a world where you have inefficiently executing applications, you have gaps in the pipeline and you can get that second thread executing. But, in efficient software, you have less opportunity to take advantage and you potentially end up with little or no gain. Some applications actually recommend turning off HT for better performance.
We will have cores, real physical cores, and that leads to better overall scalability. In heavily optimized systems, you aren’t fighting over execution pipelines because every thread has its own integer core. There is less system overhead involved in parsing out the threads because cores are all pretty much equal.
Take this scenario: a 4 core processor with HyperThreading with have all 4 physical cores actively handling threads. Now you need to execute a 5th thread. Do you put that thread on an already active core, reducing the processing of the thread already on that core because the two threads now have to share the same execution pipeline, or, do you wait a cycle and hope that one of those cores frees up? There is a lot more decision making when you have “big cores and HT cores”, but in the AMD world, you could have 8 or 16 cores, so the 5th thread just goes onto the next available physical core. It is much easier and much more scalable.
Users:
“Please explain why having two separate integer cores is better than one fat one. For example, if each core has two ALUs and two AGUs and 16 KB of L1 cache, what if it was one integer core with 4 ALUs and 4 AGUs and 32KB cache? Theoretically, you’d get about the same performance for multi-threaded programs and better single threaded performance.” – Ryan
AMD:
We get asked that a lot. The key is that a single core that would be able to compete with the throughput of two smaller cores would consume a disproportionate amount of die space and consume more power. Taking Bulldozer and turning each module into one “big core” instead of two cores with some shared resources would net you a disproportionately higher price and disproportionately higher power consumption.
In reality what we are doing is driving efficiency. And don’t worry about the single threaded performance –we have already stated publicly that Bulldozer single threaded performance is expected to be higher than our current core architectures.
What you have to keep in mind is that we are bringing innovation and driving towards the future. Back in 2005 when we did the first x86 dual core processors, there were some that argued that single core processors were better because a.) they had higher clock speed and b.) no applications really take advantage of multiple cores. Where are those people today?
When we innovated with bringing x86-64 to the market there were those that said 32-bit applications were better because they were faster and nobody really needs to access more than 2GB in most cases anyway. Where are those people today?
In this business you can either look out the windshield and focus on the road ahead and the technology that is coming up in the future or look in the rear view mirror and constantly obsess about how things were in the past.
The rules are changing now, just as they did in the past. AMD will continue to innovate.