Intel's Ivy Bridge Architecture Exposed
by Anand Lal Shimpi on September 17, 2011 2:00 AM EST- Posted in
- CPUs
- Intel
- Ivy Bridge
- IDF 2011
- Trade Shows
Power Efficiency Improvements
When Intel introduced its 22nm tri-gate transistors Intel claimed that it could see an 18% increase in performance at 1V compared to its 32nm process. At the same switching speed however, Intel's 22nm transistors can run at 75 - 80% of the voltage of their 32nm counterparts. Ivy Bridge's process alone should account for some pretty significant power savings. In addition to process however, there are a few architectural changes in IVB that will reduce power consumption.
Lower System Agent Voltages
Sandy Bridge introduced the System Agent, a name that used to refer to the uncore of a processor but now refers to the display output, memory controller, DMI and PCI Express interfaces. As of Sandy Bridge, the L3 cache was no longer included in the uncore and thus it wasn't a part of the System Agent.
The System Agent operates on a separate voltage plane than the rest of the chip. On Ivy Bridge Intel now offers even lower System Agent voltage options for the lower voltage SKUs, which in turn helps power optimize those SKUs.
More Accurate Voltage Characterization
Today Intel defines three different voltages for every Sandy Bridge CPU: LFM, nominal and turbo. LFM is the lowest frequency the CPU can run at (e.g. completely idle), nominal is the frequency it is specified to run at (e.g. 3.3GHz for a 2500K) and turbo is the highest available turbo frequency (e.g. 3.7GHz for a 2500K). Intel determines the lowest voltage possible for each one of those frequencies. Sandy Bridge obviously runs at more than just three frequencies, there are many more intermediate frequencies that it may run at depending on the current workload. The voltages at those intermediate frequencies are interpolated from the three points that I mentioned above.
With Ivy Bridge, Intel characterizes even more points along the frequency curve. Intel didn't reveal exactly how many points but it's more than three. A curve is then fit to the frequency/voltage data and depending on IVB's operating frequency a more accurate voltage point is calculated. The result from all of this seemingly simple work is a reduction in core voltage at these intermediate frequencies. Voltage changes have a cubic affect on power, so even a small reduction here can have a tangible impact. One of the points that wasn't previously characterized was max thread turbo. Ivy Bridge should be more power efficient in cases where you have all cores active.
Power Aware Interrupt Routing
This next feature is pretty neat. Ivy Bridge has logic to properly route interrupt requests to cores that are already awake vs. those that are asleep in their lowest power states. Obviously this approach can save a lot of power, however it may rob those active cores of some performance. IVB will allow prioritizing performance as well. Interrupt handling can thus be handled similarly to how it is today, or optimally for power savings.
Configurable TDP
I already wrote about what this is but if you missed our Pipeline post on it I'll briefly recap. All CPUs ship with a rated thermal design point (TDP) that tells OEMs what sort of cooling the chip requires. Traditionally that TDP value remained static and the CPU could do whatever it wanted but exceed that value. Ivy Bridge introduces configurable TDP that allows the platform to increase the CPU's TDP if given additional cooling, or decrease the TDP to fit into a smaller form factor.
The cTDP up mode is obviously for docked notebooks. You can imagine an Ivy Bridge notebook with an optional dock that could enhance the cooling capabilities of the machine. When undocked the notebook's processor would operate at a max TDP of 17W, for example, but toss it in a dock with additional cooling and the TDP would jump up to 33W. It's up to the OEMs to decide how they want to take advantage of this feature. It could be something as simple as a mobile dock with more fans, or something as complex as a modular water cooling solution with a bigger radiator in the dock. I haven't seen any concepts of systems that take advantage of Ivy Bridge's cTDP up support, but that's the theory.
What about cTDP down? Take the same 17W Ivy Bridge CPU from above but now drop the TDP to 13W, which in turn limits clock speed and voltage. Why would you want to do this? From the OEM perspective, Intel's TDP choices may seem arbitrary. Downwards configurable TDP allows OEMs to get a lower power configuration without forcing Intel to create a new SKU. OEMs can do this today through undervolting/underclocking of their own, but the cTDP down spec will at least give OEMs a guarantee of performance/power.
Configurable TDP obviously only applies to mobile Ivy Bridge. In particular the ultra low voltage and extreme edition parts will support cTDP. The cTDP values are listed in the table below:
| Ivy Bridge Configurable TDP | |||||
| cTDP Down | Nominal | cTDP Up | |||
| Ivy Bridge ULV | 13W | 17W | 33W | ||
| Ivy Bridge XE | 45W | 55W | 65W | ||
The most interesting are the 17W ULV Ivy Bridge parts as far as I'm concerned. Today you do sacrifice clock speed to get into the form factor of a MacBook Air. A clever OEM armed with Ivy Bridge might be able to deliver a cooling dock that would give you the best of both worlds: an ultra portable chassis on the go, and higher clock speeds while docked.
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Arnulf - Sunday, September 18, 2011 - link
"Voltage changes have a cubic affect on power, so even a small reduction here can have a tangible impact."P = V^2/R
Quadratic relationship, rather than cubic ?
damianrobertjones - Sunday, September 18, 2011 - link
" As we've already seen, introducing a 35W quad-core part could enable Apple (and other OEMs) to ship a quad-core IVB in a 13-inch system."Is Apple the only company that can release a 13" system?
medi01 - Monday, September 19, 2011 - link
No. But it's the only one that absolutely needs to be commented on in orgasmic tone in US press (and big chunk of EU press too)JonnyDough - Monday, September 19, 2011 - link
They're the only ones who will market it with a flashy Apple logo light on a pretty aluminum case. Everyone knows that lightweight pretty aluminum cases are a great investment on a system that is outdated after just a few years. I wish Apple would make cars instead of PCs so we could bring the DeLorean back. Something about that stainless steel body just gets me so hot. Sure, it would get horrible gas mileage and be less safe in an accident. But it's just so pretty! Plus, although it would use a standard engine made by Ford or GM under the hood, its drivers would SWEAR that Apple builds its own superior hardware!cldudley - Sunday, September 18, 2011 - link
Am I the only one who thinks Intel is really wasting a lot of time and money on improvements to their on-die GPU? They keep adding features and improvements to the onboard video, right up to including DirectX 11 support, but isn't this really all an excersise in futility?Ultimately a GPU integrated with the CPU is going to be bottlenecked by the simple fact that it does not have access to any local memory of it's own. Every time it rasterizes a triangle or performs a texture operation, it is doing it through the same memory bus the CPU is using to fetch instructions, read and write data, etc.
I read that the GPU is taking a larger proportion of the die space in Ivy Bridge, and all I see is a tragic waste of space that would have been better put into another (pair of?) core or more L1/L2 cache.
I can see the purpose of integrated graphics in the lowest-end SKUs for budget builds, and there are certainly power and TDP advantages, and things like Quick-Sync are a great idea, but why stuff a GPU in a high-end processor that will be blown away by a comparatively middle-of-the-road discrete GPU?
Death666Angel - Sunday, September 18, 2011 - link
I disagree. AMD has shown that on-die GPUs can already compete with middle-of-the-road discrete graphics in notebooks. Trinity will probably take on middle-of-the-road in the current desktop space.Your memory bandwidth argument also doesn't seem to be correct, either. Except for some AMD mainboard graphics with dedicated sideport memory, all IGPs use the RAM, but a lot of them are doing fine. It is also nice to finally see higher clocked RAM be taken advantage of (see Llano 1666MHz vs 1800MHz). DDR4 will add bandwidth as well.
Once the bandwidth becomes a bottleneck, you can address that, but at the moment Intel doesn't seem to be there, yet, so they keep addressing their other GPU issues. What is wrong with that?
Also, how many people who buy high-end CPUs end up gaming 90% of the time on them? A lot of people need high-end CPUs for work related stuff, coding, CAD etc. Why should they have to buy a discrete graphics card?
Overall, you are doing a lot of generalization and you don't take into account quite a few things. :-)
cldudley - Sunday, September 18, 2011 - link
Ironically I spend lots of time in AutoCAD, and a discrete graphics board makes a tremendous difference. Gamer-grade stuff is usually not the best thing in that arena though, it needs to be the special "workstation" cards, which have very different drivers. Quadro or FireGL.I agree with you on the work usage, and gaming workloads not being 90% of the time, but on the other hand,workstations tend to have Xeons in them, with discrete graphics cards.
platedslicer - Sunday, September 18, 2011 - link
As a fraction of the computer market, buyers who want power over everything else have plunged. Mobility is so important for OEMs now that fitting already-existent performance levels into smaller, cheaper devices becomes more important than pushing the envelope. I still remember a time when hardly anybody gave a rat's ass about how much power a CPU consumed as long as it didn't melt down. Today, power consumption is a crucial factor due to battery life and heat.Personally these developments make me rather sad, partly because I like ever-shinier games, and (more importantly) because seeing the unwashed masses talk about computers as if they were clothing brands makes me want to rip out their throats. That's how the world works, though. Hopefully the chip makers will realize that there's still a market for power over fluff.
Looking at it on the bright side, CPU power stagnation might make game designers pay more attention to content. Hey, you have to look on the bright side of life.
KPOM - Monday, September 19, 2011 - link
I think that's largely because for the average consumer, PCs have reached the point where CPU capabilities are no longer the bottleneck. Look at the success of the 2010 MacBook Air, which had a slow C2D but a speedy SSD, and sold well enough to last into mid-2011. Games are the next major hurdle, but that's the GPU rather than the CPU, and hence the reason it receives a bigger focus in Ivy Bridge (as it also did in Sandy Bridge compared to Westmere).The emphasis now is having the power we have last longer and be available in smaller, more portable devices.
JonnyDough - Monday, September 19, 2011 - link
You're missing the point. They aren't trying to beef the power of the CPU. CPUs are already quite powerful for most tasks. They are trying to lower energy usage and sell en-mass to businesses that use thousands of computers.