Managing Idle Power: Introducing ZeroCore Power

AMD has been on an idle power crusade for years now. Their willingness to be early adopters of new memory standards has allowed them to offer competitive products on narrower (and thereby cheaper) memory buses, but the tradeoff is that they get to experience the problems that come with the first revision of any new technology.

The most notable case where this has occurred would be the Radeon HD 4870 and 4890, the first cards to use GDDR5. The memory performance was fantastic; the idle power consumption was not. At the time AMD could not significantly downclock their GDDR5 products, resulting in idle power usage that approached 50W. Since then Cypress introduced a proper idle mode, allowing AMD to cut their idle power usage to 27W, while AMD has continued to further refine their idle power consumption.

With the arrival of Southern Islands comes AMD’s latest iteration of their idle power saving technologies. For 7970 AMD has gotten regular idle power usage down to 15W, roughly 5W lower than it was on the 6900 series. This is accomplished through a few extra tricks such as framebuffer compression, which reduce the amount of traffic that needs to move over the relatively power hungry GDDR5 memory bus.

However the big story with Southern Islands for idle power consumption isn’t regular idle, rather it’s “long idle.” Long idle is AMD’s term for any scenarios where the GPU can go completely idle, that is where it doesn’t need to do any work at all. For desktop computers this would primarily be for when the display is put to sleep, as the GPU does not need to do at work when the display itself can’t show anything.

Currently video cards based on AMD’s GPUs can cut their long idle power consumption by a couple of watts by turning off any display transmitters and their clock sources, but the rest of the GPU needs to be minimally powered up. This is what AMD seeks to change.

With Southern Islands AMD is introducing ZeroCore Power, their long idle power saving technology. By implementing power islands on their GPUs AMD can now outright shut off most of the functional units of a GPU when the GPU is going unused, leaving only the PCIe bus interface and a couple other components active. By doing this AMD is able to reduce their power consumption from 15W at idle to under 3W in long idle, a power level low enough that in a desktop the power consumption of the video card becomes trivial. So trivial in fact that with under 3W of heat generation AMD doesn’t even need to run the fan – ZeroCore Power shuts off the fan as it’s rendered an unnecessary device that’s consuming power.

Ultimately ZeroCore Power isn’t a brand new concept, but this is the first time we’ve seen something quite like this on the desktop. Even AMD will tell you the idea is borrowed from their mobile graphics technology, where they need to be able to power down the GPU completely for power savings when using graphics switching capabilities. But unlike mobile graphics switching AMD isn’t fully cutting off the GPU, rather they’re using power islands to leave the GPU turned on in a minimal power state. As a result the implementation details are very different even if the outcomes are similar. At the same time a technology like this isn’t solely developed for desktops so it remains to be seen how AMD can leverage it to further reduce power consumption on the eventual mobile Southern Islands GPUs.

Of course as impressive as sub-3W long idle power consumption is on a device with 4.3B transistors, at the end of the day ZeroCore Power is only as cool as the ways it can be used. For gaming cards such as the 7970 AMD will be leveraging it not only as a way to reduce power consumption when driving a blanked display, but more importantly will be leveraging it to improve the power consumption of CrossFire. Currently AMD’s Ultra Low Power State (ULPS) can reduce the idle power usage of slave cards to a lower state than the master card, but the GPUs must still remain powered up. Just as with long idle, ZeroCore Power will change this.

Fundamentally there isn’t a significant difference between driving a blank display and being a slave card card in CrossFire, in both situations the video card is doing nothing. So AMD will be taking ZeroCore Power to its logical conclusion by coupling it with CrossFire; ZeroCore Power will put CrossFire slave cards in ZCP power state whenever they’re not in use. This not only means reducing the power consumption of the slave cards, but just as with long idle turning off the fan too. As AMD correctly notes, this virtually eliminates the idle power penalty for CrossFire and completely eliminates the idle noise penalty. With ZCP CrossFire is now no noisier and only ever so slightly more power hungry than a single card at idle.

Furthermore the benefits of ZCP in CrossFire not only apply to multiple cards, but multiple-GPU cards too. When AMD launches their eventual multi-GPU Tahiti card the slave GPU can be put in a ZCP state, leaving only the master GPU and the PCIe bridge active. Coupled with ZCP on the master GPU when in long idle and even a beastly multi-GPU card should be able to reduce its long idle power consumption to under 10W after accounting for the PCIe bridge.

Meanwhile as for load power consumption, not a great deal has changed from Cayman. AMD’s PowerTune throttling technology will be coming to the entire Southern Islands lineup, and it will be implemented just as it was in Cayman. This means it remains operationally the same by calculating the power draw of the card based on load, and then altering clockspeeds in order to keep the card below its PowerTune limit. For the 7970 the limit is the same as it was for the 6970: 250W, with the ability to raise or lower it by 20% in the Catalyst Control Center.

On that note, at this time the only way to read the core clockspeed of the 7970 is through AMD’s drivers, which don’t reflect the current status of PowerTune. As a result we cannot currently tell when PowerTune has started throttling. If you recall our 6970 results we did find a single game that managed to hit PowerTune’s limit: Metro 2033. So we have a great deal of interest in seeing if this holds true for the 7970 or not. Looking at frame rates this may be the case, as we picked up 1.5fps on Metro after raising the PowerTune limit by 20%. But at 2.7% this is on the edge of being typical benchmark variability so we’d need to be able to see the core clockspeed to confirm it.

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  • Wreckage - Thursday, December 22, 2011 - link

    That's kind of disappointing. Reply
  • atticus14 - Thursday, December 22, 2011 - link

    oh look its that guy that was banned from the forums for being an overboard nvidia zealot. Reply
  • medi01 - Tuesday, January 03, 2012 - link

    Maybe he meant "somebody @ anandtech is again pissing on AMDs cookies"?

    I mean "oh, it's fastest and coolest single GPU card on the market, it is slightly more expensive than competitor's, but it kinda sucks since AMD didn't go "significantly cheaper than nVidia" route" is hard to call unbiased, eh?

    Kind of disappointing conclusion, indeed.
    Reply
  • ddarko - Thursday, December 22, 2011 - link

    To each their own but I think this is undeniable impressive:

    "Even with the same number of ROPs and a similar theoretical performance limit (29.6 vs 28.16), 7970 is pushing 51% more pixels than 6970 is" and

    "it’s clear that AMD’s tessellation efficiency improvements are quite real, and that with Tahiti AMD can deliver much better tessellation performance than Cayman even at virtually the same theoretical triangle throughput rate."
    Reply
  • Samus - Thursday, December 22, 2011 - link

    I prefer nVidia products, mostly because the games I play (EA/DICE Battlefield-series) are heavily sponsered by nVidia, giving them a developement-edge.

    That out of the way, nVidia has had their problems just like this card is going to experience. Remember when Fermi came out, it was a performance joke, not because it was slow, but because it used a ridiculous amount of power to do the same thing as an ATI card while costing substantially more.

    Fermi wasn't successful until second-generation products were released, most obviously the GTX460 and GT430, reasonably priced cards with quality drivers and low power consumption. But it took over a year for nVidia to release those, and it will take over a year for ATI to make this architecture shine.
    Reply
  • kyuu - Thursday, December 22, 2011 - link

    Wat? The only thing there might be an issue with is drivers. As far as power consumption goes, this should be better than Cayman. Reply
  • CeriseCogburn - Sunday, March 11, 2012 - link

    He's saying the 28mn node will have further power improvements. Take it as an amd compliment - rather you should have. Reply
  • StriderTR - Thursday, December 22, 2011 - link

    EA/Dice are just as heavily sponsored by AMD, more in fact. Not sure where your getting your information, but its .. well ... wrong. Nvidia bought the rights to advertize the game with their hardware, AMD is heavily sponsoring BF3 and related material. Example, The Controller.

    Also, the GTX 580 and HD 6970 perform within a few FPS of each other on BF3. I run dual 6970's, by buddy runs dual 580's, we are almost always within 2 FPS of one and other at any given time.

    AMD will have the new architecture "shining" in far under a year. They have been focused on it for a long time already.

    Simple bottom line, both Nvidia and AMD make world class cards these days. No matter your preference, you have cards to choose from that will rock any games on the planet for a long time to come.
    Reply
  • deaner - Thursday, December 22, 2011 - link

    Umm, yea no. Not so much with nvidia and EA/DICE Batttlefield series giving nvidia a development edge. (if it does, the results are yet to be seen)
    Facts are facts, the 5 series to our current review today, the 7970, do and again continue to edge the Nvidia lines. The AMD Catalyst performance of particular note, BF3, has been far superior.

    Reply
  • RussianSensation - Thursday, December 22, 2011 - link

    ."..most obviously the GTX460 and GT430, reasonably priced cards with quality drivers and low power consumption. But it took over a year for nVidia to release those"

    GTX470/480 launched March 26, 2010
    GTX460 launched July 12, 2010
    GT430 launched October 11, 2010

    Also, Fermi's performance at launch was not a joke. GTX470 delivered performance between HD5850 and HD5870, priced in the middle. Looking now, GTX480 ~ HD6970. So again, both of those cards did relatively well at the time. Once you consider overclocking of the 470/480, they did extremely well, both easily surprassing the 5870 in performance in overclocked states.

    Sure power consumption was high, but that's the nature of the game for highest-end GPUs.
    Reply

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