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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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  • Roland00Address - Wednesday, December 15, 2010 - link

    1) The architecture article is something that can be written before hand, or written during benching (if the bench is on a loop). It has very little "cramming" to get out right after a NDA ends. Anand knows this info for a couple of weeks but can't discuss it due to NDAs. Furthermore the reason anandtech is one of the best review sites on the net is the fact they do go into the architecture details. The architecture as well as the performance benchmarks is the reason I come to anandtech instead of other review sites as my first choice.

    2) The spelling and grammar errors is a common thing at anandtech, this is nothing new. That said I can't complain for my spelling and grammar is far worse than Ryan's.

    If you don't like the style of the review go somewhere else.
    Reply
  • Ryan Smith - Wednesday, December 15, 2010 - link

    1) That's only half true. AMD told us the basics about the 6900 series back in October, but I never had full access to the product information (and more importantly the developers) until 1 week ago. So this entire article was brought up from scratch in 1 week.

    It's rare for us to get too much access much earlier than that; the closest thing was the Fermi launch where NVIDIA was willing to talk about the architecture months in advance. Otherwise that's usually a closely held secret in order to keep the competition from having concrete details too soon.
    Reply
  • Dracusis - Wednesday, December 15, 2010 - link

    Neither the AMD 6xxx series or Nvidia's 5xx series have been added. Would like to see how my 4870x2 stack up against this latest generation and weather or not it's worth upgrading. Reply
  • Makaveli - Wednesday, December 15, 2010 - link

    The Canadian pricing on these cards are hilarious.

    Ncix is taking preorder for the 6970 at $474.

    While they sell the 570 for $379.

    Can someone explain to me why I would pay $100 more for the radeon when the 570 gives equal performance?

    Are these retailers that retarded?
    Reply
  • stangflyer - Thursday, December 16, 2010 - link

    They will price the 6950/6970 high for a few days to get the boys that bleed red and have to have the new cards right away to pay top dollar for the card.

    After a week they will probably be about the same price.
    Reply
  • Ryan Smith - Thursday, December 16, 2010 - link

    Bench will be up to date by the start of next week. Reply
  • Paladin1211 - Thursday, December 16, 2010 - link

    Whats wrong with you rarson? Do you even know whats the difference between "Graphics card review", "Performance review", "Performance Preview"? I dont know how good your grammar and spelling are, but they dont matter as long as you cant understand the basic meaning of the words.

    Most of the sites will tell you about WHAT, but here at AnandTech, you'll truly find out WHY and HOW. Well, of course, you can always go elsewhere try to read some numbers instead of words.

    Keep up the good works, Ryan.
    Reply
  • Belard - Thursday, December 16, 2010 - link

    The 3870 and 3850 were the TOP end for ATI, as was the 4800 and the 5800. Their relationship of model numbers do not have anything to do with the status of Nvidia.

    When the 3870 was brand new, what was the HIGHEST end card ATI had back then? Oh yeah, the 3870!

    4800 is over the 3870, easily.
    4600 replaced the 3800

    The 5800s replaces the 4800s... easily.
    the 5700s kind of replaced the 4800s.

    The 6800s replaces the 5700 & 5800s, the 6900s replace the 5800s, but not so much on performance.

    I paid $90 for my 4670 and a much better value than the $220 3870 since both cards perform almost the same.
    Reply
  • AmdInside - Thursday, December 16, 2010 - link

    I can't think of a single website that has better hardware reviews, at least for computer technology than Anandtech. Ryan, keep up the great work. Reply
  • George.Zhang - Thursday, December 16, 2010 - link

    BTW, HD6950 looks great and affordable for me. Reply

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