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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  • gevorg - Thursday, December 22, 2011 - link

    37.9dB is a horrible testbed for noise testing! WTF! Reply
  • mavere - Thursday, December 22, 2011 - link

    Seriously!

    With the prevalence of practically silent PSUs, efficient tower heatsinks, and large quiet fans, I cannot fathom why the noise floor is 37.9 dB.
    Reply
  • Finally - Thursday, December 22, 2011 - link

    As usual, AT is shooting straight for the brain-dam, I mean, ENTHUSIAST crowd feat. a non-mentioned power supply that should be well around 1000W in order to drive over-priced CPUs as well as quadruple GPU setups.
    If you find that horrendous they will offer you not to read this review, but their upcoming HTPC review where they will employ the same 1000W power supply...
    Reply
  • B3an - Thursday, December 22, 2011 - link

    *face palm*

    1: 1000+ Watt PSU's are normally more quiet if anything as they're better equipped to deal with higher power loads. When a system like this uses nowhere near the PSU's full power the fan often spins at a very low RPM. Some 1000+ PSU's will just shut the fan off completely when a system uses less than 30% of it's power.

    2: It's totally normal for a system to be around 40 dB without including the graphics cards. Two or 3 fans alone normally cause this much noise even if they're large low RPM fans. Then you have noise levels from surroundings which even in a "quiet" room are normally more than 15 dB.

    3: Grow some fucking brain cells kids.
    Reply
  • andymcca - Thursday, December 22, 2011 - link

    1) If you were a quiet computing enthusiast, you would know that the statement
    "1000+ Watt PSU's are normally more quiet if anything"
    is patently false. 1000W PSUs are necessarily less efficient at realistic loads (<600W at full load in single GPU systems). This is a trade-off of optimizing for efficiency at high wattages. There is no free lunch in power electronics. Lower efficiency yields more heat yields more noise, all else being equal. And I assure you that a high end silent/quiet PSU is designed for low air flow and uses components at least as high in quality as their higher wattage (non-silent/non-quiet) competitors. Since the PSU is not decribed (a problem which has been brought up many times in the past concerning AT reviews), who knows?

    2) 40dB is fairly loud if you are aiming for quiet operation. Ambient noise in a quiet room can be roughly 20dB (provided there is not a lot of ambient outdoor noise). 40dB is roughly the amplitude of conversation in a quiet room (non-whispered). A computer that hums as loud as I talk is pretty loud! I'm not sure if you opinion is informed by any empirical experience, but for precise comparison of different sources the floor should be at minimum 20dB below the sources in question.

    3) You have no idea what the parent's age or background is, but your comment #3 certainly implies something about your maturity.
    Reply
  • formulav8 - Tuesday, February 21, 2012 - link

    Seriously grow up. Your a nasty mouth as well. Reply
  • piroroadkill - Thursday, December 22, 2011 - link

    Haha, yeah.

    Still, I guess we have to leave that work to SPCR.
    Reply
  • Kjella - Thursday, December 22, 2011 - link

    High-end graphics cards are even noisier, so who cares? A 250W card won't be quiet no matter what. Using an overclocked Intel Core i7 3960X is obviously so the benchmarks won't be CPU limited, not to make a quiet PC. Reply
  • Ryan Smith - Thursday, December 22, 2011 - link

    Our testing methodology only has us inches from the case (an open case I should add), hence the noise from our H100 closed loop radiator makes itself known. In any case these numbers aren't meant to be absolutes, we only use them on a relative basis. Reply
  • MadMan007 - Thursday, December 22, 2011 - link

    [AES chart] on page 7? Reply

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