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Thread: Intel vs. AMD Performance-Per-Watt On Ubuntu 14.04 Linux

  1. #41
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    Quote Originally Posted by vick View Post
    Maybe my English isn't very good. I'm sorry. I was using those terms like they're equal. Should I have said performance/Watt (operations/Joule) or performance per Watt / operations per Joule (this looks more confusing to me though)?
    Performance per Watt and Operations per Joule are equivalent, as I already showed in a previous post. But what you are apparently missing is that total energy consumed to perform a given computational task (such as a compilation) is ALSO EQUIVALENT to Performance per Watt and Operations per Joule, as long as the computational task is fixed. Which, of course, it is for a compilation (well, there could be a slight variation if the compiler has to do slightly different optimizations for each CPU, but that is likely a small enough variation to ignore).

  2. #42
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    Will these graphs be updated or should I do what tuke81 did for the other tests? I guess I can grab the numbers and use Octave to make myself some easy to read bar graphs.

  3. #43
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    Quote Originally Posted by guido12 View Post
    Will these graphs be updated or should I do what tuke81 did for the other tests?
    I wouldn't hold my breath. This isn't the first time Michael posts obviously wrong performance-per-watt results, people complained, provided the correct formulas to use and yet here's another bad set of results. And I'm sure it's not the last either, so if you'd like to actually post the correct results I'm also interested in that

  4. #44
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    Quote Originally Posted by H.F.P View Post
    The confusion comes from the term "power consumption". Many people think "power consumption" to be equal to "energy consumption". In fact, the energy consumption is the integral of power consumption over time. Therefore your complaint is more about the fact that you would like to see a conclusion about "energy consumption". On the other hand, the problem with energy consumption comes with workloads that usually run "forever" or at least not with a fixed amount of time e.g., playing a computer game. For the latter, power consumption can be treated equivalent to energy consumption.

    Anyhow, it can't be repeated often enough: consuming a little bit more power over a much shorter duration still holds a lower energy consumption.
    What are you talking about? These graphs are wrong no matter what you call it. It's precisely because of what you say in your last sentence that it's obvious that the graphs are wrong. When two cpus take the same time to finish a task but one of them uses 40W more power (or energy, or whatever you want to call it) to do it, then it's obviously a lot less power efficient. These graphs show the complete opposite!

  5. #45

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    Quote Originally Posted by guido12 View Post
    Will these graphs be updated or should I do what tuke81 did for the other tests?
    I doubt it. I've never seen Michael fix an article, no matter how egregious the error.

    I actually came here to post a comment about the graph fail, but was gratified to see that everybody is already all over it.

    Seriously, how could those graphs in the article ever have been published? They're so obviously, obviously wrong. You don't even have to think - they leap out and slap you around the head with a wet fish.

    Finally, (physicist here) I'd like to see two values plotted:

    Performance per Watt = benchmark result / (average power * time / time) = benchmark result / average power over task (units of per Watt)
    Energy needed per task = average power * time taken (units of Joules)

    Of course, the performance per Watt formula assumes higher is better, so for those benchmarks where lower is better you'd need to use 1/result or something for the performance.

  6. #46
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    Quote Originally Posted by baffledmollusc View Post

    Finally, (physicist here) I'd like to see two values plotted:

    Performance per Watt = benchmark result / (average power * time / time) = benchmark result / average power over task (units of per Watt)
    Energy needed per task = average power * time taken (units of Joules)

    Of course, the performance per Watt formula assumes higher is better, so for those benchmarks where lower is better you'd need to use 1/result or something for the performance.
    The first formula does not make sense. The benchmark result is in seconds, so you would be looking at units of seconds per Watt (not "per Watt"), and that is useless. If you change the benchmark result to be "1/result" then you would have units of (1/sec) / (Joule/sec) = 1 / Joule. But that would just be the reciprocal of "Energy needed per task", so it does not provide any new information over just the Energy required for the computation.

    I'm not sure why people keep suggesting all sorts of strange metrics. The only important metric here for power efficiency is the total energy required to complete the task. Of course, it is also useful to know how quickly the task is completed, and that is already provided by the "Time to Compile" benchmark.

    Bottom line is that this type of benchmark should include two values for each CPU: energy required to complete task, and time required to complete task.
    Last edited by jwilliams; 01-18-2014 at 08:00 PM.

  7. #47
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    Quote Originally Posted by baffledmollusc View Post
    (average power * time / time)
    really? :-D

  8. #48
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    Quote Originally Posted by devius View Post
    I wouldn't hold my breath. This isn't the first time Michael posts obviously wrong performance-per-watt results, people complained, provided the correct formulas to use and yet here's another bad set of results. And I'm sure it's not the last either, so if you'd like to actually post the correct results I'm also interested in that
    Quote Originally Posted by baffledmollusc View Post
    I doubt it. I've never seen Michael fix an article, no matter how egregious the error.

    I actually came here to post a comment about the graph fail, but was gratified to see that everybody is already all over it.

    Seriously, how could those graphs in the article ever have been published? They're so obviously, obviously wrong. You don't even have to think - they leap out and slap you around the head with a wet fish.

    Finally, (physicist here) I'd like to see two values plotted:

    Performance per Watt = benchmark result / (average power * time / time) = benchmark result / average power over task (units of per Watt)
    Energy needed per task = average power * time taken (units of Joules)

    Of course, the performance per Watt formula assumes higher is better, so for those benchmarks where lower is better you'd need to use 1/result or something for the performance.
    That's unfortunate. I haven't been a reader for very long but I've regarded Phoronix as a professional Linux oriented site despite being run by only one person. Even people from industry seem to post in these forums (at least looking at their forum titles). So I thought article updates to fix mistakes would be done. I guess that's why I haven't seen titles with "(Update)" or similar in them like I do with other sites.

    I guess I'll go slap something in Octave because I'm interested in this article's subject for the new mini-ITX PC I plan on building. I haven't completely decided on Kaveri or Haswell yet.

  9. #49

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    Quote Originally Posted by droste View Post
    really? :-D
    Yes, really.

    Say you get a benchmark score of 80 FLOPS, iterations, whatever. Say it took 30 seconds, and the CPU used an average power of 50W over that time. So

    Performance per Watt = benchmark result / (average power * time / time)

    = 80 FLOPS / (50W * 30s / 30s)
    = 80 FLOPS / 50W
    = 1.6 FLOPS / W
    = 1.6 FLOPS per Watt

    The reason I wrote it that way is average power * time = energy, and to get a power you have to divide by time taken.

    Although now I look at it, I'm prepared to agree that while correct, it's not the most straightforward approach. I think the issue is I always think in terms of energy, and convert that to whatever later.

  10. #50
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    Quote Originally Posted by baffledmollusc View Post
    I doubt it. I've never seen Michael fix an article, no matter how egregious the error.
    Actually the original post of *this* article had an error which Michael fixed right after someone reported it -- a second copy of one of the graphs instead of the perf/watt chart.

    http://phoronix.com/forums/showthrea...046#post390046

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