AMD Discloses Bobcat & Bulldozer Architectures at Hot Chips 2010
by Anand Lal Shimpi on August 24, 2010 1:33 AM ESTBranch Prediction and a Deeper Pipeline
Bulldozer will use a deeper pipeline with less logic per stage compared to current Phenom II/Opteron processors. AMD argues that this will ensure clock speed won’t be a problem with the design and we should expect to see Bulldozer based products at similar if not higher clock speeds than what we have today with Phenom II.
With a deeper pipe, branch prediction becomes more important and Bulldozer has a significant change in the way branch prediction works.
In Phenom II, the branch prediction and instruction fetch logic are run in lockstep - when one stalls, the other also stalls. Branches are predicted as they are encountered. If the fetch logic grabs an x86 branch instruction, the prediction logic works in parallel to predict the likely target of that branch. However if the branch is incorrectly predicted, subsequent branches aren’t predicted until the current mispredict is correctly resolved. As a result, the fetch logic and prefetchers can’t work and potential performance is lost.
In Bulldozer the branch prediction and fetch logic are decoupled. The predictor now produces a queue of future fetch addresses. Even if there’s a mispredict the branch predictor can continue to fill its prediction queue with targets. The fetch logic can then check this queue of addresses against what’s in the instruction cache to avoid future misses in L1.
Prefetchers
With Phenom AMD implemented comparable prefetching logic to what Intel did with Core. In Bulldozer, AMD is ramping up the aggressiveness of those prefetchers. There are independent prefetchers at both the L1 and L2 levels that support larger numbers of strides and large stride sizes (both compared to what exists in current AMD architectures). There’s also a non-strided data prefetcher that looks at correlated cache misses and uses that data to prefetch into the caches.
AMD unfortunately didn’t go into more detail on its prefetchers other than to promise that they are much more aggressive than what we have today. Aggressive prefetching usually means there’s a good amount of memory bandwidth available so I’m wondering if we’ll see Bulldozer adopt a 3 - 4 channel DDR3 memory controller in high end configurations similar to what we have today with Gulftown.
Power Gating & Real Turbo Mode
Each Bulldozer module in a processor can be clocked and power gated independently. This has two implications. You can now power off cores (in sets of two) that aren’t in use and save tons of idle power. You can also use the power savings to drive up the frequency of other cores in a Bulldozer CPU. With Bulldozer, AMD should have something functionally equivalent to Intel’s Turbo Boost modes. Since clock speed and power gating is controlled at the module level and not the core level there will still be some differences between the two but this should be much better than AMD’s current Core Turbo technology.
There’s of course extensive clock gating around the chip, but obviously the big change is power gating which AMD hasn’t had up to this point (Bobcat is also power gated).
Performance and Availability
While Bobcat is going to be in production in Q4 of this year, with system availability in Q1 of 2011 - Bulldozer is still a 2011 project and AMD isn’t giving any guidance as to when in 2011.
Parts are already back and in AMD’s labs but we have no indication of performance or rollout schedule. Given Bobcat’s schedule, I’d say that the first Bulldozer CPUs will be out no earlier than Q2 2011 and AMD’s unwillingness to specify what half of the year would imply that it’ll be a late Q2/early Q3 launch.
The first Bulldozer parts will be server focused, with high end desktop CPUs following but still in 2011.
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stalker27 - Wednesday, August 25, 2010 - link
Those "some of you" don't make them R&D money... which, silly boy that you are... got you those fast chips in the first place.Oh boy, how important some people think they are.
iwod - Tuesday, August 24, 2010 - link
Deleted:iwod - Tuesday, August 24, 2010 - link
I am not a Professional Engineer, but i do have my degree in Electrics Engineering. I fully understand how Models and Simulations, MatLabs, Video Encoding, or CG Rendering requires as much Performance as it can get.But to the world, I am sorry you are right. You are exactly not counted in "the rest of the world". You are inside a professional niche whether you like it or not. That includes even Hardcore PC gamers, which is shrinking day by day due to completion from consoles. No this is not to say PC Gaming to going to die. It just means it is getting smaller. And this trend is not going to change until something dramatic happens.
The rest of the world, counted by BILLIONS, are moving, or looking to move to iPad, Netbook, Cheap Notebook, or something that just get things done as cheaply as possible. It is the reason why Netbook took off. Why Atom based All in One PC took off. No one in the marketing department knew such Gigantic market exists.
Lastly, i want to emphasis, by the "world" i really mean the World. Not an American view of the world which would just literally be America by itself. China, India, Brazil, and even countries like Japan are having trouble selling high end PC.
jabber - Wednesday, August 25, 2010 - link
Yep, all you computer engineer folks and render farms etc. account for a very small minority in the "world of computer users". You are not mainstream users.In general terms the world isnt really that interested anymore in CPU performance improvements.
Most folks out there just want smaller and lower power so they can carry a computer around with them. They dont give a damn what the CPU architecture is.
The leviathan CPU approach by AMD and Intel could go the way of the dinosaur for mainstream computing. ARM could well be the new mainstream CPU leader in just five years.
Just think outside your own little box.
B3an - Wednesday, August 25, 2010 - link
Ridiculous small minded comment.Render farms and the like may not be mainstream, but gaming is, then theres things like video encoding, servers, workstations, databases, all very popular mainstream stuff that millions of people use and the internet also relies on.
A very large percentage of computer users will always want faster CPU's.
If Intel or AMD did what you think most people want, then nothing would progress either. No 3D interfaces, no artificial intelligence, no anything, as the power needed for it would never be there.
BitJunkie - Wednesday, August 25, 2010 - link
It all comes down to usage models right? The point is that AMD and Intel are trying to capture as many usage models as possible within a given architecture.This is why modular design is kind of appealing - you can bolt stuff together to hit the desired spot in the thermal-computational envelope.
The thing that "engineers" fall foul of is that there is a divergence going on. On the one hand general computing is dominating, with a desire to drive down power usage. On the other hand there is the same appetite for improved computational performance as we get smarter and more ambitious in the way we tackle engineering problems.
The issue is that both camps are looking to the same architecture for answers.
The reason why that doesnt work for me is that some computations just don't benefit from parallelism - more cores doesn't mean more productivity. Therefore I want to see the few cores that I do use become super efficient at flipping bits on a floating point calculation.
Right now there's no clear answer to that problem - but it will probably come with Fusion and the point at which the GPU takes the role that math co-processors did before being swallowed into the CPU. For this to work we need Microsoft to handle the GPU compute stuff natively within windows so that existing code can execute and not think about what part of the hardware is lifting the load.
Therefore my sincere hope is that GPUs will become the new math co-processors and Windows 8 will make that happen.
Oh, and there's no need for any tribalism here wrt to usage models. It's all good.
jabber - Wednesday, August 25, 2010 - link
No its not small minded. Its looking at the big picture.The big picture is that for most users their CPU power needs were reached and surpassed some time ago.
CPUs are not the bottle neck in modern PCs. Storage systems are.
We need better, cheaper and faster storage.
I've been pushing out 1.6Ghz dual core Atoms to 95% of my small business customers and a good chunk of domestics for the past year.
I havent had one moan or complaint that the PCs were not fast enough. Very few customers are hardcore gamers. Gamers are still a small subsection of the computing world.
I'm not asking AMD/Intel to stop research in new and faster CPU designs. Keep going boys its all good.
I'm just saying that the majority of mainstream computing lays along a very different path going forward to those that require power at all costs.
Not all of us need octa-cores at 4Ghz+. A lot of us can get by with a 2Ghz dual core and a half decent 7200rpm HDD.
Most of the PCs I see are still single core. Folks are managing just fine right now.
Plenty folks are now managing with just 1Ghz or less on a mobile device. Thats why Intel are taking ARM more seriously as they see that future mainstream being more low power, mobile based than leviathan mega-core-mega-wattage beasts.
Things will change rapidly over the next three or four years.
Aries1470 - Friday, August 27, 2010 - link
Quote:"We need better, cheaper and faster storage.
I've been pushing out 1.6Ghz dual core Atoms to 95% of my small business customers and a good chunk of domestics for the past year.
I havent had one moan or complaint that the PCs were not fast enough. Very few customers are hardcore gamers. Gamers are still a small subsection of the computing world.
Well, I for one totally agree. I purchaed last year an Atom 330 dual core, and it does more than enough.
I already had a much more powerful system, of which I use about.... one or twice a month if that! It is a quad core, has 4 gigs and a 2gb 9600 gpu.
I have moved away from gaming and encoding and all that stuff.
The motherboard I have is:
ATOM-GM1-330 of which I imported to Australia from the U.S.A., since the distibuter here does not bring this model.
I have paired it with 4Gb of memory, but using only 3gb, since I am running 32bit systems (XP & win 7)
A Blu-ray writer....
and a LP 5450 used with an adapter from 16x -> 1x
It plays blu-ray great while browsing at the same time!
I browse the internet at the same time as my wife and kid watch a movie on the 50" plasma, with NO stutter.
Needless to say, I got it as a secondary pc... and has become my main pc. It is left on basically 24/7, with NO fan on the cpu! Low power consumption too.
It performs great for the functions I want, and can even play Civ IV on it... but not much else. If I want to play real gaming, I use my other pc.
So for what it is, it works great for my needs! No useless power consumption, does its Boinc too, albeit slow, but still better than my older P2-550... that was still alive a few years ago.
Most people I know, don't use their pc for gaming anymore, mostly for facebook/ twitter and video calling, they have their Wii's & Xbox and one has a PS3...
Ok, end of rant, but to conclude, I concur, your average Joe, has his gaming machine, and his pc is for htpc or not a gaming power pc.
gruffi - Thursday, August 26, 2010 - link
Sandy Bridge, the architecture that is suppose to leap again like Pentium 4 to C2D? Thanks for the joke of the day.Sandy Bridge looks more like a minor update of Nehalem/Westmere. More load/store bandwidth, improved cache, AVX and maybe a few other little tweaks. Nothing special. I think it will be less of an improvement as Core 2 (Core successor) and Nehalem (Core 2 successor) were.
In many ways Bulldozer looks superior to what Intel has to offer in 2011.
Lonbjerg - Tuesday, August 24, 2010 - link
I don't care for "Bobcat"...mediocre performance in a cramped formfactor (netbooks) have as much interest to me as being dragged naked across field filled with broken glass.The "Bulldozer" looks fine on paper...problem is that so did Phenom.
I look forward to the real reviews, and not PR slices :)