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Performance Per Watt

AMD's Radeon HD 5000-Series: Measuring Power Efficiency
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By comparing graphics card performance and power consumption, we can get an idea of energy efficiency. We of course have to measure performance to do this. Ideally, we use the same settings and resolutions for all graphics cards tested, divide the results (either in the form of frame rate or benchmark score) by the power consumed. For example, we can run Crysis using the Very High detail settings at 1920x1080 on a test platform with various graphics cards, such as the Radeon HD 5670, HD 5770 and HD 5870. Simultaneously, we record peak power consumption numbers during those runs. Compare the two numbers, and you get the performance per watt for each graphics card in that one application.

This approach does have some disadvantages. First, the benchmark has to scale perfectly with processing power, which doesn’t always happen. Such synthetic cases don't translate well to the real world, where variables like processing power and  bus bandwidth/latency come into play. Second, you have to choose settings that are conservative enough to allow the lowest-performing contender to still run well enough. If we were to use the above-mentioned settings, frame rates would hardly be ideal for gameplay (well below 30 FPS). Third, the results are only relevant to the application tested. If the software we test scales well and emphasizes the GPU, we won’t see the same results in an application that's CPU/system limited.

We can try to address some of those inherent limitations. By nature and design, the cards will likely fall into groups separated by playable frame rates at different resolutions. So, a high-enough quality setting will only be playable at low resolutions on more mainstream cards, while boards with more graphics processing horsepower will be able to offer the same frame rate at higher resolutions. Frame buffer capacity will come into play, particularly at very high resolutions. Once the cards fall into place, power consumption measurements will tell us which card requires more power to be playable at a certain resolution. Then it's just a matter of picking the card that offers the best performance with the least power consumed.  

These measurements will work, but they do not tell us the whole story. They will only tell us the typical power consumption of graphics cards running games, which can make use of all GPU resources. Thus, we’ll also run a handful of other applications and workloads capable of giving us a more complete picture of power consumption and efficiency.

Efficiency At Idle

Outside of playing games or running Direct3D and OpenGL applications, the GPU is hardly used. Not surprisingly, we’d expect the graphics processor’s power consumption to dip as low as possible in these situations. This is why we measure idle power consumption.

Idle measurements are typically recorded on the desktop when the PC isn’t running any other applications. That means the results aren’t reflective of power consumption when a piece of software that uses the GPU is left idling. Cinema 4D is a good example.

Power Consumption In Different Scenarios

What if we wanted to know exactly how much power is consumed in situations that fall in between the maximum load and minimum idle numbers we record for most GPU reviews? What kind of power draw we can expect? This is the focus of today’s story.

We believe there is more to graphics card power consumption and energy efficiency than what can be gleamed from power consumption numbers at the two extremes. By measuring power consumption and performance running various GPU applications, we get a better understanding of overall efficiency.

Today, we're looking at a handful of graphics solutions from AMD--the Radeon HD 5770, HD 5670, HD 5870 1 GB, and HD 5870 2 GB. As a reference point, we’re using a Radeon HD 3300, an integrated GPU included with AMD's 790GX chipset, and an older Radeon 2900 XT. These two references were chosen for different reasons. The Radeon HD 3300 integrated graphics is a good baseline with no discrete graphics installed at all. The Radeon 2900 XT offers roughly the performance of today's DX11 mainstream cards. Using it, we are able to ascertain the architectural improvements made by AMD’s latest-generation design, affecting overall performance per watt.

There is one minor consideration to bear in mind as you look at the power measurement results: variation between samples. In discussing this piece with AMD, company representatives made it a point to mention that variations from  one card to another exist. They may be due to the components used, board design, and even the graphics chip itself. Your own efficiency testing may consequently look a little different from what we have here.

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Top Comments
  • 18 Hide
    Lutfij , August 24, 2010 9:23 AM
    ^ nvidia would loose at this battle. period.
  • 14 Hide
    tony singh , August 24, 2010 6:32 AM
    Very innovative article tom keep it up!! Similar article consisting of various cpus would be really useful.
Other Comments
  • 14 Hide
    tony singh , August 24, 2010 6:32 AM
    Very innovative article tom keep it up!! Similar article consisting of various cpus would be really useful.
  • 3 Hide
    tacoslave , August 24, 2010 6:59 AM
    gtx 480 and 460 for reference?
  • 18 Hide
    Lutfij , August 24, 2010 9:23 AM
    ^ nvidia would loose at this battle. period.
  • 3 Hide
    spidey81 , August 24, 2010 11:20 AM
    I know the FPS/watt wouldn't be as good, but what if the 5670 was crossfired. Would it still be a better alternative, efficiency wise, than say a 5850?
  • 0 Hide
    nforce4max , August 24, 2010 11:50 AM
    Remember the R600 (2900xt) has a 80nm core while the 5870 has a 45nm core. Shrink the R600 and you will get the 3870 (55nm) that barely uses hardly any.
  • 7 Hide
    rhino13 , August 24, 2010 12:34 PM
    And now just for fun we should compare to Fermi.

    Oh, wait, this just in:
    Quote:
    There is a Fermi comparison chart that was avalible but you needed to have two screens to display the bar graph for Fermi's power consumption and temperature. So the decission was made to provide readers with the single screen only version.
  • 0 Hide
    aevm , August 24, 2010 12:51 PM
    I loved this part:

    Quote:
    A mere 20 watts separate the Radeon HD 3300, HD 5670, HD 5770, and HD 5870 1 GB. So, in certain cases, the Radeon HD 5870 1 GB can still save enough power to close in on its more mainstream derivatives. Again, this is the case because the cards use a fixed-function video engine to assist in decoding acceleration, which is the same from one board to the next. Thus, even a high-end card behaves like a lower-end product in such a workload. This is very important, as you will see later on.


    My next PC will be used mostly for movie DVDs and Diablo 3. Apparently if I get a 5870 1GB I get the best of both worlds - speed in Diablo and low power consumption when playing movies.

    How about nVidia cards, would I get the same behavior with a GTX 480 for example?
  • -2 Hide
    Onus , August 24, 2010 12:57 PM
    For those not needing the absolute maximum eye candy at high resolutions in their games, the HD5670 looks like a very nice choice for a do-it-all card that won't break the budget.
    Next questions: First, where does the HD5750 fall in this? Second, if you do the same kinds of manual tweaking for power saving that you did in your Cool-n-Quiet analysis, how will that change the results? And finally, if you run a F@H client, what does that do to "idle" scores, when the GPU is actually quite busy processing a work unit?
  • 0 Hide
    eodeo , August 24, 2010 1:34 PM
    Very interesting article indeed.

    I'd love to see nvidia cards and beefier CPUs used as well. Normal non green hdds too. Just how big of a difference in speed/power do they make?

    Thank you for sharing.
  • 3 Hide
    arnawa_widagda , August 24, 2010 3:42 PM
    Hi guys,

    Thanks for reading the article.

    Quote:
    Next questions: First, where does the HD5750 fall in this? Second, if you do the same kinds of manual tweaking for power saving that you did in your Cool-n-Quiet analysis, how will that change the results? And finally, if you run a F@H client, what does that do to "idle" scores, when the GPU is actually quite busy processing a work unit?


    Have no 5750 sample yet, but they should relatively be close to 5770. For this article, we simply chose the best bin for each series (Redwood, Juniper and Cypress).

    The second question, what will happen when you tweak the chip? Glad you ask!! I can't say much yet, but you'll be surprised what the 5870 1 GB can do.

    As for NVIDIA cards, I'm hoping to have the chance to test GF100 and derivatives very soon.

    Take care.

  • 0 Hide
    JohnnyLucky , August 24, 2010 4:03 PM
    Thanks for including mainstream applications.

    Interesting comments about Furmark.

  • 0 Hide
    xbsoft , August 24, 2010 6:24 PM
    >> TEST SYSTEM: AMD Phenom II X4 955 Black Edition (3.2 GHz, >>>>>> 8
  • -2 Hide
    mattmock , August 24, 2010 6:30 PM
    Quote:
    It just means you typically will never encounter such an extreme usage scenario.

    I have to disagree, there are several ways a user can fully load their graphics card in normal use. I have found that my GPU utilization and fan speed go to %100 when I play the dice mini-game in The Witcher. The game only has to render a small game board and the frame rate goes into the 200-300 range. Some thing similar occurs when I hit the pause key in stalker.
  • 0 Hide
    Fokissed , August 24, 2010 11:03 PM
    xbsoft(3.2 GHz, >>>>>> 8

    bad penis joke?
  • 1 Hide
    MartenKL , August 24, 2010 11:13 PM
    FPS/watt uses average FPS during the test but max wattage? I am very disappointed by this flawed logic from toms hardware. Spending an entire page describing why everyone else uses flawed testing for benchmarking power efficiency and then doing this simple error is just embarrassing.
  • 1 Hide
    MartenKL , August 24, 2010 11:30 PM
    I forgot to say I am very interested in this kind of benchmarks and I am glad Toms Hardware is writing a big piece on it, sorry for the harsh words. For me total Wh per completed task for the entire system is the most interesting number. To me that is the only way to measure efficiency. add to that idle power draw and every user can calculate their own usage (by adding tasks and idle hours). Sorry and thanks yet again for an article with a very important topic. My interest is noise and mechanical wear rather than power cost and environment.
  • 0 Hide
    tubers , August 25, 2010 2:50 AM
    Fermi comparison please :) 
  • 0 Hide
    mayne92 , August 25, 2010 2:45 PM
    What a great article by Tom's (Arnawa)! Probably one of the best articles I have read in a long time! Enjoyed the article because was very detailed and you explained everything so well and I LOVE my tech reviews! A Fermi comparison would have been nice but I know that you said that you don't have them to play with so it's said as a request. Hats off to you Arnawa...for a great read...
  • 0 Hide
    eddieroolz , August 25, 2010 11:07 PM
    Really paints in perspective the power of GPUs compared to CPUs. I really wish that one day we'll be able to use the GPU for central processing.
  • 0 Hide
    EDIGX2 , August 26, 2010 6:00 PM
    Hello everyone
    Well i think this article inspired form the movie that AMD has release lately.
    That movie called as i think "Mis understanding"here's the link: http://www.youtube.com/watch?v=2QkyfGJgcwQ
    As we all know AMD is innovative in power consumption as well It's Graphics I read such this review in Anandtech.com ...Just WOW....Loads Of Noise and power flowed for Fermi VGAs . In this review we see the smooth performance for 5670 and 5770.
    and another thing that we should give a hint on is You know releasing Fermi after six month of releasing 5000 series...I think it's good in performance but not after 6 Months!!! but awful in power consuming and noise and heat!!
    Take care guys
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