PowerTune, Cont

PowerTune’s functionality is accomplished in a two-step process. The first step is defining the desired TDP of a product. Notably (and unlike NVIDIA) AMD is not using power monitoring hardware here, citing the costs of such chips and the additional design complexities they create. Instead AMD is profiling the performance of their GPUs to determine what the power consumption behavior is for each functional block. This behavior is used to assign a weighted score to each functional block, which in turn is used to establish a rough equation to find the power consumption of the GPU based on each block’s usage.

AMD doesn’t provide the precise equations used, but you can envision it looking something like this:

Power Consumption =( (shaderUsage * shaderWeight) + (ropUsage * ropWeight) + (memoryUsage * memoryWeight) ) * clockspeed

In the case of the Radeon HD 6970, the TDP is 250W, while the default clockspeed is 880MHz.

With a power equation established, AMD can then adjust GPU performance on the fly to keep power consumption under the TDP. This is accomplished by dynamically adjusting just the core clock based on GPU usage a few times a second. So long as power consumption stays under 250W the 6970 stays at 880MHz, and if power consumption exceeds 250W then the core clock will be brought down to keep power usage in check.

It’s worth noting that in practice the core clock and power usage do not have a linear relationship, so PowerTune may have to drop the core clock by quite a bit in order to maintain its power target. The memory clock and even the core voltage remain unchanged (these are only set with PowerPlay states), so PowerTune only has the core clock to work with.

Ultimately PowerTune is going to fundamentally change how we measure and classify AMD’s GPUs. With PowerTune the TDP really is the TDP; as a completely game/application agonistic way of measuring and containing power consumption, it’s simply not possible to exceed the TDP. The power consumption of the average game is still below the TDP – sometimes well below – so there’s still an average case and a worst case scenario to discuss, but the range between them just got much smaller.

Furthermore as a result, real world performance is going to differ from theoretical performance that much more. Just as is the case with CPUs where the performance you get is the performance you get; teraFLOPs, cache bandwidth, and clocks alone won’t tell you everything about the performance of a product. The TDP and whether the card regularly crosses it will factor in to performance, just as how cooling factors in to CPU performance by allowing/prohibiting higher turbo modes. At least for AMD’s GPUs, we’re now going to be talking about how much performance you can get for any given TDP instead of specific clockspeeds, bringing performance per watt to the forefront of importance.

So by now you’re no doubt wondering what the impact of PowerTune is, and the short answer is that there’s virtually no impact. We’ve gone ahead and compiled a list of all the games and applications in our test suite, and whether they triggered PowerTune throttling. Of the dozen tests, only two triggered PowerTune: FurMark as expected, and Metro 2033. Furthermore as you can see there was a significant difference between the average clockspeed of our 6970 in these two situations.

AMD Radeon HD 6970 PowerTune Throttling
Game/Application Throttled?
Crysis: Warhead No
BattleForge No
Metro Yes (850Mhz)
HAWX No
Civilization V No
Bad Company 2 No
STALKER No
DiRT 2 No
Mass Effect 2 No
Wolfenstein No
3DMark Vantage Yes
MediaEspresso 6 No
Unigine Heaven No
FurMark Yes (600MHz)
Distributed.net Client No

In the case of Metro the average clockspeed was 850MHz; Metro spent 95% of the time running at 880MHz, and only at a couple of points did the core clock drop to around 700MHz. Conversely FurMark, a known outlier, drove the average core clock down to 600MHz for a 30% reduction in the core clock. So while PowerTune definitely had an impact on FurMark performance it did almost nothing to Metro, never mind any other game/application. To illustrate the point, here are our Metro numbers with and without PowerTune.

Radeon HD 6970: Metro 2033 Performance
PowerTune 250W PowerTune 300W
2560x1600 25.5 26
1920x1200 39 39.5
1680x1050 64.5 65

The difference is no more than .5fps on average, which may as well be within our experimental error range for this benchmark. For everything we’ve tested on the 6970 and the 6950, the default PowerTune settings do not have a meaningful performance impact on any game or application we test. Thus at this point we’re confident that there are no immediate drawbacks to PowerTune for desktop use.

Ultimately this is a negative feedback mechanism, unlike Turbo which is a positive feedback mechanism. Without overclocking the best a 6970 will run at is 880MHz, whereas Turbo would increase clockspeeds when conditions allow. Neither one is absolutely the right way to do things, but there’s a very different perception when performance is taken away, versus when performance is “added” for free. I absolutely like where this is going – both as a hardware reviewer and as a gamer – but I’d be surprised if this didn’t generate at least some level of controversy.

Finally, while we’ve looked at PowerTune in the scope of desktop usage, we’ve largely ignored other cases so far. AMD will be the first to tell you that PowerTune is more important for mobile use than it is desktop use, and mobile use is all the more important as the balance between desktops and laptops sold continues to slide towards laptops. In the mobile space not only does PowerTune mean that AMD will absolutely hit their TDPs, but it should allow them to produce mobile GPUs that come with higher stock core clocks, comfortable in the knowledge that PowerTune will keep power usage in check for the heaviest games and applications. The real story for PowerTune doesn’t even begin until 2011 – as far as the 6900 series is concerned, this may as well be a sneak peak.

Even then there’s one possible exception we’re waiting to see: 6990 (Antilles). The Radeon HD 5970 put us in an interesting spot: it was and still is the fastest card around, but unless you can take advantage of CrossFire it’s slower than a single 5870, a byproduct of the fact that AMD had to use lower core and memory clocks to make their 300W TDP. This is in stark comparison to the 4870X2, which really was 2 4870s glued together with the same single GPU performance. With PowerTune AMD doesn’t necessarily need to repeat the 5970’s castrated clocks; they could make a 6970X2, and let PowerTune clip performance as necessary to keep it under 300W. If something is being used without CrossFire for example, then there’s no reason not to run the 1 GPU at full speed. It would be the best of both worlds.

In the meantime we’re not done with PowerTune quite yet. PowerTune isn’t just something AMD can set – it’s adjustable in the Overdrive control panel too.

Redefining TDP With PowerTune Tweaking PowerTune
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  • cyrusfox - Wednesday, December 15, 2010 - link

    You should totally be able to do a 4X1 display, 2 DP and 2 DVI, as long as one of those DP dells also has a DVI input. That would get rid of the need for your usb-vga adapter. Reply
  • gimmeagdlaugh - Wednesday, December 15, 2010 - link

    Not sure why AMD 6970 has green bar,
    while NV 580 has red bar...?
    Reply
  • medi01 - Wednesday, December 15, 2010 - link

    Also wondering. Did nVidia marketing guys called again? Reply
  • Ryan Smith - Wednesday, December 15, 2010 - link

    I normally use green for new products. That's all there is to it. Reply
  • JimmiG - Wednesday, December 15, 2010 - link

    Still don't like the idea of Powertune. Games with a high power load are the ones that fully utilize many parts of the GPU at the same time, while less power hungry games only utilize parts of it. So technically, the specifications are *wrong* as printed in the table on page one.

    The 6970 does *not* have 1536 stream processors at 880 MHz. Sure, it may have 1536 stream processors, and it may run at up to 880 MHz.. But not at the same time!

    So if you fully utilize all 1536 processors, maybe it's a 700 MHz GPU.. or to put it another way, if you want the GPU to run at 880 MHz, you may only utilize, say 1200 stream processors.
    Reply
  • cyrusfox - Wednesday, December 15, 2010 - link

    I think Anand did a pretty good job of explaining at how it reasonably power throttles the card. Also as 3rd party board vendors will probably make work-arounds for people who abhor getting anything but the best performance(even at the cost of efficiency). I really don't think this is much of an issue, but a good development that is probably being driven by Fusion for Ontario, Zacate, and llano. Also only Metro 2033 triggered any reduction(850Mhz from 880Mhz). So your statement of a crippled GPU only holds for Furmark, nothing got handicapped to 700Mhz. Games are trying to efficiently use all the GPU has to offer, so I don't believe we will see many games at all trigger the use of powertune throttling. Reply
  • JimmiG - Wednesday, December 15, 2010 - link

    Perhaps, but there's no telling what kind of load future DX11 games, combined with faster CPUs will put on the GPU. Programs like Furmark don't do anything unusual, they don't increase GPU clocks or voltages or anything like that - they just tell the GPU - "Draw this on the screen as fast as you can".

    It's the same dilemma overclockers face - Do I keep this higher overclock that causes the system to crash with stress tests but works fine with games and benchmarks? Or do I back down a few steps to guarantee 100% stability. IMO, no overclock is valid unless the system can last through the most rigorous stress tests without crashes, errors or thermal protection kicking in.

    Also, having a card that throttles with games available today tells me that it's running way to close to the thermal limit. Overclocking in this case would have to be defined as simply disabling the protection to make the GPU always work at the advertised speed.
    It's a lazy solution, what they should have done is go back to the drawing board until the GPU hits the desired performance target while staying within the thermal envelope. Prescott showed that you can't just keep adding stuff without any considerations for thermals or power usage.
    Reply
  • AnnihilatorX - Wednesday, December 15, 2010 - link

    Didn't you see you can increase the throttle threshold by 20% in Catalyst Control Centre. This means 300W until it throttles, which in a sense disables the PowerTune. Reply
  • Mr Perfect - Thursday, December 16, 2010 - link

    On page eight Ryan mentions that Metro 2033 DID get throttled to 700MHz. The 850MHz number was reached by averaging the amount of time Metro was at 880MHz with the time it ran at 700MHz.

    Which is a prime example of why I hate averages in reviews. If you have a significantly better "best case", you can get away with a particularly bad "worst case" and end up smelling like roses.
    Reply
  • fausto412 - Wednesday, December 15, 2010 - link

    CPU's have been doing this for a while...and you are allowed to turn the feature off. AMD is giving you a range to go over.

    It will cut down on RMA's, Extend Reliability.
    Reply

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