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Redefining TDP With PowerTune

One of our fundamental benchmarks is FurMark, oZone3D’s handy GPU load testing tool. The furry donut can generate a workload in excess of anything any game or GPGPU application can do, giving us an excellent way to establish a worst case scenario for power usage, GPU temperatures, and cooler noise. The fact that it was worse than any game/application has ruffled both AMD and NVIDIA’s feathers however, as it’s been known to kill older cards and otherwise make their lives more difficult, leading to the two companies labeling the program a “power virus”.

FurMark is just one symptom of a larger issue however, and that’s TDP. Compared to their CPU counterparts at only 140W, video cards are power monsters. The ATX specification allows for PCIe cards to draw up to 300W, and we quite regularly surpass that when FurMark is in use. Things get even dicier on laptops and all-in-one computers, where compact spaces and small batteries limit how much power a GPU can draw and how much heat can effectively be dissipated. For these reasons products need to be designed to meet a certain TDP; in the case of desktop cards we saw products such as the Radeon HD 5970 where it had sub-5870 clocks to meet the 300W TDP (with easy overvolting controls to make up for it), and in laptop parts we routinely see products with many disabled functional units and low clocks to meet those particularly low TDP requirements.

Although we see both AMD and NVIDIA surpass their official TDP on FurMark, it’s never by very much. After all TDP defines the thermal limits of a system, so if you regularly surpass those limits it can lead to overwhelming the cooling and ultimately risking system damage. It’s because of FurMark and other scenarios that AMD claims that they have to set their products’ performance lower than they’d like. Call of Duty, Crysis, The Sims 3, and other games aren’t necessarily causing video cards to draw power in excess of their TDP, but the need to cover the edge cases like FurMark does. As a result AMD has to plan around applications and games that cause a high level of power draw, setting their performance levels low enough that these edge cases don’t lead to the GPU regularly surpassing its TDP.

This ultimately leads to a concept similar to dynamic range, defined by Wikipedia as: “the ratio between the largest and smallest possible values of a changeable quantity.” We typically use dynamic range when talking about audio and video, referring to the range between quiet and loud sounds, and dark and light imagery respectively. However power draw is quite similar in concept, with a variety of games and applications leading to a variety of loads on the GPU. Furthermore while dynamic range is generally a good thing for audio and video, it’s generally a bad thing for desktop GPU usage – low power utilization on a GPU-bound game means that there’s plenty of headroom for bumping up clocks and voltages to improve the performance of that game. Going back to our earlier example however, a GPU can’t be set this high under normal conditions, otherwise FurMark and similar applications will push the GPU well past TDP.

The answer to the dynamic power range problem is to have variable clockspeeds; set the clocks low to keep power usage down on power-demanding games, and set the clocks high on power-light games. In fact we already have this in the CPU world, where Intel and AMD use their turbo modes to achieve this. If there’s enough thermal and power headroom, these processors can increase their clockspeeds by upwards of several steps. This allows AMD and Intel to not only offer processors that are overall faster on average, but it lets them specifically focus on improving single-threaded performance by pushing 1 core well above its normal clockspeeds when it’s the only core in use.

It was only a matter of time until this kind of scheme came to the GPU world, and that time is here. Earlier this year we saw NVIDIA lay the groundwork with the GTX 500 series, where they implemented external power monitoring hardware for the purpose of identifying and slowing down FurMark and OCCT; however that’s as far as they went, capping only FurMark and OCCT. With Cayman and the 6900 series AMD is going to take this to the next step with a technology called PowerTune.

PowerTune is a power containment technology, designed to allow AMD to contain the power consumption of their GPUs to a pre-determined value. In essence it’s Turbo in reverse: instead of having a low base clockspeed and higher turbo multipliers, AMD is setting a high base clockspeed and letting PowerTune cap GPU performance when it exceeds AMD’s TDP. The net result is that AMD can reduce the dynamic power range of their GPUs by setting high clockspeeds at high voltages to maximize performance, and then letting PowerTune cap GPU performance for the edge cases that cause GPU power consumption to exceed AMD’s preset value.

Advancing Primitives: Dual Graphics Engines & New ROPs PowerTune, Cont
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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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