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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Dustin Sklavos - Tuesday, August 24, 2010 - link
If you're encoding using Adobe software, ditch AMD until Bulldozer. Adobe's software makes heavy use of SSE 4.1 instructions, which current AMD chips lack, and the extra two cores don't pick up the slack compared to a fast i7.flyck - Tuesday, August 24, 2010 - link
From the design of Bulldozer's FPU it is cleared that AMD want Multi Threaded FPU to run on OpenCL.Not sure what you mean with that? (it is true they want to abuse that in the future with fusion) but at this moment i see: Sandybridge 2hreads -> one FPU, Bulldozer 2 threads -> one FPU
BitJunkie - Tuesday, August 24, 2010 - link
I think he's picking up on the point that this general purpose design is going to favour integer operations over floating point. Looking at this architecture from the perspective of someone wanting to perform a lot of floating point matrix calculus then the performance improvement of each "core" is going to be proportionally less than for integer calcs.So what he's saying is that quite clearly AMD believe that general purpose CPUs are just that and have designed for a well defined balance of FP and Interger operations i.e. If you want more FLOPS go talk to the GPU?
stalker27 - Tuesday, August 24, 2010 - link
"And if Bulldozer comes any later, it will be up against the die shrink of SandyBridge, Ivy Bridge. Things dont look so good in here."Basically, you've contradicted yourself right here:
"Most of us dont need SUPER FAST computer."
True, and true.... Ivy will probably be faster than Bulldozer (speculatively) as is Nehalem to Stars, but most people, i.e. the "cash cow" won't buy these expensive products. Instead they will focus on mid to low end computers which by their performance is more then/or enough for their needs.
So things might not look good in reviews and bench tops, but in the stores and on people's bank balances they will look pretty good.
jabber - Tuesday, August 24, 2010 - link
Hooray!I'm glad at last some folks are waking up to the fact that having the fastest or most expensive CPU means absolutely jack!
All the latest fastest CPU stuff just means a little bit more internet traffic for tech review sites.
The rest of the world doesnt give a damn.
All the real world is interested in is the best CPU for the buck in a $400 PC box to run W7 and Office on. AMD needs to get a proper marketing dept to start telling folks that.
All AMD has to do is produce good performing chips for a good price. It dosent need a CPU to beat the best of Intel.
The real world lost interest in CPU performance the minute dual cores arrived and they could finally run IE/Office and a couple of mainframe sessions without it grinding to a halt.
I bet Intel gives out more review samples of its top CPU than it sells.
JPForums - Tuesday, August 24, 2010 - link
"All the real world is interested in is the best CPU for the buck in a $400 PC box to run W7 and Office on. AMD needs to get a proper marketing dept to start telling folks that.""The real world lost interest in CPU performance the minute dual cores arrived and they could finally run IE/Office and a couple of mainframe sessions without it grinding to a halt."
Apparently us Engineers aren't part of "The rest of the world".
Try running products from the likes of Mentor Graphics, Cadence, and Synopsis for reasonably large designs. Check out what a difference each new CPU makes in PROe (assuming sufficient GPU horsepower). Run some large Matlab simulations, Visual studio compilations, and Xilinx builds. You don't even have to get out of college before you run into many of these scenarios.
Trust me when I say that we care about the next greatest thing.
An extra $1000 dollars on a CPU is easily justified when companies are billing $100+ per Engineering hour (not to be confused with take home pay).
BitJunkie - Tuesday, August 24, 2010 - link
Exactly so: An example would be a 24hr calculation to perform a detailed 3D finite element analysis. This is not unusual using highly spec'd Xeon work stations from your vendor of choice.It might take 5 to 10 days to set up a model including testing of different aspects: Mesh density, discretisation errors, boundary effects, parametric studies. The set up time with numerous supporting pre-analysis runs is what really costs. Anything we can do to reduce this is worth while.
The above would be the typical process BEFORE considering a batch-job on a HPC cluster if we wanted to look at a series of load cases etc.
Time is money.
mapesdhs - Tuesday, August 24, 2010 - link
I know a number of movie studios who love every extra bit of
CPU muscle they can get their hands on. Rendering really
hammers current hardware. One place has more than 7000
XEON cores, but it's never enough. Short of writing specialised
sw to exploit shared-memory machines that use i7 XEONs (which
has its own costs), the demand for ever higher processing
speed will always persist. Visual effects complexity constantly
increases as artists push the boundaries of what is possible.
And this is just one example market segment. As BitJunkie
suggests, these issues surface everywhere.
Another good example: the new Cosmos machine in the UK
which contains 128 x 6-core i7 XEON (Nehalem EX) with
2TB RAM (ie. 768 cores total). This is a _single system_,
not a cluster (SGI Altix UV). Nothing less is good enough for
running modern cosmological simulations. There will be
much effort by those using the system on achieving good
efficiency with 512+ cores; atm many HPC tasks don't scale
well beyond 32 to 64 cores. Point being, improving the
performance of a single core is just as important as general
core scaling for such complex tasks. SGI's goal is to produce
a next-gen UV system which will scale to 262144 cores in
a single shared-memory system (32768 x 8-core CPUs).
You can never have enough computing power. :D
Ian.
stalker27 - Wednesday, August 25, 2010 - link
You're 1% of the market... for you, Intel and AMD have reserved cherry-picked chips that they can charge you 1K for but at the same time offer you that needed speed. How's that?BTW, he said real world, not rest of the world. That makes you somewhat of an illusion. But don't take it the bad way... more like most of us would dream working in an environment full of hot setups, big projects and big bux, unlike in the real world where you have to mop the floor after debugging for 8 hours straight... if they don't force you to work extra two hours without pay, never-mind that before you start the workday you have to go to various bureaucratic public clerk offices to deal with stuff that was supposed to be taken care by secretaries... which got fired for no apparent reason some time ago.
So stop moaning... you have it good, even as 1%.
Makaveli - Tuesday, August 24, 2010 - link
lol if AMD and intel followed your logic we would all still be running Pentium 2 and socket A Athlons silly boy.You make yourself look like an ass when you make a generalized statement like that, as if you are speaking for the rest of the world.
As that other guy pointed out some of us do more than just office work on our pc's!