AMD Radeon HD 7970 Review: 28nm And Graphics Core Next, Together As One
by Ryan Smith on December 22, 2011 12:00 AM EST- Posted in
- GPUs
- AMD
- Radeon
- ATI
- Radeon HD 7000
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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Scali - Monday, December 26, 2011 - link
Lol, how's that, when I'm the one saying that AMD's cards are the best performers in Crysis 2?I'm neutral, a concept that is obviously alien to you. Idiots...
Scali - Monday, December 26, 2011 - link
Heck, I'm also the guy who made Endless City run on non-nVidia cards. How does that make me an nVidia fanboy?CeriseCogburn - Thursday, March 8, 2012 - link
That's sad when an nvidia fanboy has to help all the amd fannies with software coding so they can run a benchmark, then after all that work to help the underprivileged, nothing but attacks after the facts... finally silence them.It's really sad when the truth is so far from the pop culture mind that actually speaking it is nearly forbidden.
Thank you for helping them with the benchmark. Continue to be kind in such ways to the sour whining and disgruntled, as it only helped prove how pathetic amd dx11 was...
james007 - Friday, December 30, 2011 - link
This sounded like such an awesome card and I was psyched to get it the moment it comes out -- until reading the part about dropping the 2nd DVI port. A DisplayPort-to-SLDVI doesn't do it, for me, because my desktop has to drive two 30" displays. In fact, I would love to be able to drive a third display so I can have a touch-screen also. My current (previous-generation) VDC does drive both displays just fine.This does not seem like such an infrequent requirement, especially for high-end users. Why would they drop the ability to drive the 2nd display? !!!
Argh!
The_Countess666 - Saturday, December 31, 2011 - link
not trying to sell you anything but, HDMI to dual-link dvi does exist (see link, or google yourself for other shops).http://sewelldirect.com/hdmi-to-dvi-dual-link-cabl...
and these cards do have 1 HDMI-out so that should work for you.
Penti - Wednesday, January 4, 2012 - link
It's the IHV that makes those decisions any way, just because it's not on a reference card doesn't mean they won't show up or that you can't build a card with it. But the HDMI supports more then 1920x1200 finally on this card any how. I guess they could deliver a card with the old type of DVI>HDMI adapters. Obviously opting for HDMI and multidisplaycapable displayport 1.2 makes more sense though. It's been around for years now.Penti - Wednesday, January 4, 2012 - link
Just make sure you actually has the number of connections you need when buying the card, many 7970 bords only appear to support single-link DVI on the DVI-connector.poordirtfarmer2 - Wednesday, January 4, 2012 - link
Enjoyed the article.So this new 79XX architecture is about a GPU architecture that’s also good for “compute work”. The reference to NVIDIA ‘s professional video cards (Quadro ; Telsa), implies to me that this might mean video cards viable for use both in gaming and in engineering / video work stations.
I’m not a pro, but do a lot of video editing, rendering and encoding. I’ve avoided dedicating a machine with an expensive special purpose QUADRO video card. Am I reading the wrong thing into this review, or might the new 79XX and the right driver give folks like me the best of both worlds?
radojko - Thursday, January 5, 2012 - link
UVD 3 in NextGen is a disappointing. Nvidia is two generation in front with PureVideo HD 5.psiboy - Monday, January 9, 2012 - link
Well Mr Ryan Smith I must ask why the omission of 1920 x 1080 in al lbenchmarks... given that almost every new monitor for quite some time has been natively 1920 x 1080... what is it with you guys and Tom's lately.. you both seem to have been ignoring the reality of what most of your readers are using!