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Power Gating

With 1.45 billion transistors on die, Llano relies on extensive power gating in order to keep things in order. The APU is split into two independent power islands: the CPU and the GPU. The memory controller and North Bridge both live on the GPU's power island. Each island has its own independent voltage source.

Everything from an individual CPU core to the entire GPU or virtually the entire APU package can be power gated. AMD provided photon recombination images to show the impact power gating the GPU can have on leakage current:

Although not depicted above, Llano can also fully power gate the x86 CPU cores or both the CPU and GPU if the entire APU is in a deep sleep state. Being able to completely power gate CPU cores or the GPU is an important part of enabling the next major feature of Llano: Turbo Core.

Turbo Core

All processors whether CPUs, GPUs or APUs have to be designed to strict thermal and power limits. OEMs need to know exactly what sort of chassis they'll be able to build around these chips and as a result the chip vendors provide guidance in the form of specifications, including the chip's thermal design point (TDP).

In the old days of microprocessors things were simple. You had a single core that ran all the time and it consumed all of the available thermal budget allocated for that core. AMD and Intel eventually enabled dynamic clock frequencies which let your single core underclock itself when it wasn't being used, which helped reduce power and extend battery life. Then came the multi-core era.

CPUs couldn't just start putting out twice as much heat now that they had two cores; instead, each core had to consume less power. The chip guys achieved this by running the cores at lower frequencies and voltages than they did in the single-core days. Two cores paved the way to four cores, which meant another reduction in clock speed per core. Sure we got much better multi-threaded performance, but for single-threaded applications performance wasn't as great as it could be. Users had to make a tradeoff: good multi-threaded performance or good single-threaded performance; you couldn't have both. Until power gating came along that is.

Without power gating you can never really shut off power to an idle core. The transistors aren't switching but power is still dissipated thanks to leakage current. Remember that transistors don't simply stop conducting electricity when they're off. The smaller they get, the more leaky our beloved transistors become. Power gating lets you physically block the flow of current to the transistors that are being gated, so when they're off, they're actually off. With an idle core shut off, now you have the extra TDP headroom to run any active cores at higher frequencies.

Intel does this with a technology it calls Turbo Boost. Intel looks at current draw and thermal sensors spread out all over the chip and determines when it has the available thermal headroom to turbo up any active cores. AMD implements a similar technology in Llano (and previously in their hex-core desktop parts) called Turbo Core.

I say similar but not identical because AMD's approach differs in a very important way. While Intel looks at current draw and temperature data, AMD looks at workload. Each activity within the Llano APU is assigned a certain power weight (e.g. an integer multiply is known to require a certain amount of power). Llano is aware of the operations it's currently working on and based on the weights associated with these operations it comes up with a general estimate of its power consumption on a per core basis. I mention this is an estimate because it correlates digital activity to power consumption; it doesn't actually measure power consumption.

Based on the number of events and their individual weights, AMD estimates the power consumption of each core and determines how much TDP headroom exists in the system. If the OS is requesting the highest p-state from the CPU and there's available TDP headroom, Llano will turbo up any active cores up to a maximum frequency. Like Sandy Bridge, Llano is able to temporarily exceed the APU's maximum TDP if it determines that the recent history of power consumption has been low enough that it'll take a while for the APU to ramp up to any thermal limits.

One major limit of Llano's Turbo Core is that the GPU can't turbo up in the event of the CPU cores being idle. Only the CPU cores can turbo up if they have available headroom. I suspect future versions of Llano will probably enable GPU Turbo Core as well:

It's unclear to me at this point what shortcomings or advantages exist for AMD's Turbo Core method vs. Intel's Turbo Boost. At the bare minimum the two are finally comparable although they use different approaches to attain a similar end result. AMD doesn't yet have a method of actually displaying Turbo Core frequencies, unfortunately, so we're operating a bit blind at this point. Over time I hope to have a better idea of how AMD's solution stacks up.

The GPU Introducing Mobile Llano
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  • DanNeely - Tuesday, June 14, 2011 - link

    Just looking at transistor count misses most of the story. The highly repetitive layout in the GPU allows for much denser transistor layout, the die is only 5% larger. That's close enough that factors like yield and raw per wafer cost become at least as important. Reply
  • Lunyone - Tuesday, June 14, 2011 - link

    Looks like we're finally getting close to having integrated graphics good enough for some good light gaming :) Hopefully these won't be priced to high to sell. There are sooo many Sandy Bridge based laptops out there that are within the $500-600 price range it isn't even funny. I hope we can get the top of the line Llano for about $600-650. I think the C50 or E-350 have been relegated down to tablet only now, since Llano is where it's at now. Reply
  • ET - Tuesday, June 14, 2011 - link

    Brazos will likely keep its place at the lower price point and smaller size laptops. It would be interesting to see if the larger E-350 laptops will be replaced by Llano or will survive. I was surprised they were even introduced, but it's possible that if people are buying them they will continue to do so.

    Still, I'm hoping that Llano can make it into small form factor laptops.
    Reply
  • Beenthere - Tuesday, June 14, 2011 - link

    I am definitely ready to buy a Llano powered laptop. I suspect Llano will suit the needs of the largest notebook segment and deliver better graphics at a lower price point. AMD is bound to take notebook market share from Intel. I wouldn't ever consider an Intel product. Reply
  • RussianSensation - Tuesday, June 14, 2011 - link

    What? The largest notebook segment doesn't care about GPUs in a laptop. Look at Apple - a non-gaming platform more or less - and quarter after quarter has the highest growth in the notebook market share. The fact that Intel HD graphics command #1 market share in the mobile and desktop space also shows that the the majority of consumers don't care about mobile graphics beyond watching HD content.

    So with Llano you get a GPU that's still only fast enough for 1368x768 resolution gaming at the lowest settings and CPU performance that's only as fast as a Q6700 from 2007. Llano only makes sense if you are on a budget to buy a laptop. If you care about CPU performance, it's too slow. If you care about GPU performance, it's again too slow. So the only customer it will find is a niche one until they can create an APU with Bulldozer cores inside and a much faster GPU.

    We have also seen a significant surge in consumers that desire premium made notebooks. Llano designs will likely be relegated to cheap looking and cheap quality laptops. Certainly it wont be able to compete with Ultrabooks.

    I am almost certain that most of today's consumers will care about screen resolution, an SSD, the quality of the screen/materials build quality of the laptop before even thinking about the fact that Llano's GPU is faster than Intel's. Then there is AMD's past history of having unimpressive mobile CPUs over the last 5+ years. It's going to take 2-3 generations before consumers even think about switching brands in such a scenario. Most people will just buy an Intel based SB notebook simply because Intel has made the best mobile processor for the last "forever".

    This is a good step for AMD, but they have a long road ahead.
    Reply
  • duploxxx - Tuesday, June 14, 2011 - link

    The share count is no longer relevant since an IGP is deployed anyhow with each system, while there are many delivered with discrete it still counts as an IGP also.

    Have a look at your so called apple highest growth market... it ships with discrete ATI graphics.....

    Actually most don't know that the IGP is crappy, they are fooled by adiot sales and large electronic vendors who try to push there margins.

    THis is the introduction generation that will shed some light, just look at the brazos also, it has been a success and even atom refresh wil not be able to take this back.
    Reply
  • nickb64 - Tuesday, June 14, 2011 - link

    arguably the most popular Apple laptop, the 13" Pro, now ships with Intel Integrated graphics, not discrete ATI/AMD graphics

    Overall, you're right, but I just wanted to point out that Intel is probably getting a pretty solid boost out of 13" MBP sales this year.
    Reply
  • jjj - Tuesday, June 14, 2011 - link

    lol that's quite something to give Apple as an example for what the average user needs.Macs are niche products and will remain so without fundamental strategy changes.

    ps:how outraged would you be if tomorrow the new Air shows up with a Llano in it?
    pps:today's average consumer makes a few hundreds $ per month and is not looking for high resolution (not that he knows wtf resolution is anyway) or SSD.
    Reply
  • RussianSensation - Tuesday, June 14, 2011 - link

    Intel wouldn't ship Air with Llano, not until they can deliver Bulldozer cores. Why would they ship a laptop with 50% slower CPU speed and go backwards? Not to mention, they'd lose Thunderbolt if they ditched SB. Reply
  • mino - Tuesday, June 14, 2011 - link

    Thunderbolt is PCIe. Reply

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