Power Consumption

TDP or not the TDP, That is The Question

Notice: When we initially posted this page, we ran numbers with an ASRock Z370 board. We have since discovered that the voltage applied by the board was super high, beyond normal expectations. We have since re-run the numbers using the MSI MPG Z390 Gaming Edge AC motherboard, which does not have this issue.

As shown above, Intel has given each of these processors a Thermal Design Power of 95 Watts. This magic value, as mainstream processors have grown in the last two years, has been at the center of a number of irate users.

By Intel’s own definitions, the TDP is an indicator of the cooling performance required for a processor to maintain its base frequency. In this case, if a user can only cool 95W, they can expect to realistically get only 3.6 GHz on a shiny new Core i9-9900K. That magic TDP value does not take into account any turbo values, even if the all-core turbo (such as 4.7 GHz in this case) is way above that 95W rating.

In order to make sense of this, Intel uses a series of variables called Power Levels: PL1, PL2, and PL3.

That slide is a bit dense, so we should focus on the graph on the right. This is a graph of power against time.

Here we have four horizontal lines from bottom to top: cooling limit (PL1), sustained power delivery (PL2), battery limit (PL3), and power delivery limit.

The bottom line, the cooling limit, is effectively the TDP value. Here the power (and frequency) is limited by the cooling at hand. It is the lowest sustainable frequency for the cooling, so for the most part TDP = PL1.  This is our ‘95W’ value.

The PL2 value, or sustained power delivery, is what amounts to the turbo. This is the maximum sustainable power that the processor can take until we start to hit thermal issues. When a chip goes into a turbo mode, sometimes briefly, this is the part that is relied upon. The value of PL2 can be set by the system manufacturer, however Intel has its own recommended PL2 values.

In this case, for the new 9th Generation Core processors, Intel has set the PL2 value to 210W. This is essentially the power required to hit the peak turbo on all cores, such as 4.7 GHz on the eight-core Core i9-9900K. So users can completely forget the 95W TDP when it comes to cooling. If a user wants those peak frequencies, it’s time to invest in something capable and serious.

Luckily, we can confirm all this in our power testing.

For our testing, we use POV-Ray as our load generator then take the register values for CPU power. This software method, for most platforms, includes the power split between the cores, the DRAM, and the package power. Most users cite this method as not being fully accurate, however compared to system testing it provides a good number without losses, and it forms the basis of the power values used inside the processor for its various functions.

Starting with the easy one, maximum CPU power draw.

Power (Package), Full Load

Focusing on the new Intel CPUs we have tested, both of them go beyond the TDP value, but do not hit PL2. At this level, the CPU is running all cores and threads at the all-core turbo frequency. Both 168.48W for the i9-9900K and 124.27W for the i7=9700K is far and above that ‘TDP’ rating noted above.

Should users be interested, in our testing at 4C/4T and 3.0 GHz, the Core i9-9900K only hit 23W power. Doubling the cores and adding another 50%+ to the frequency causes an almost 7x increase in power consumption. When Intel starts pushing those frequencies, it needs a lot of juice.

If we break out the 9900K into how much power is consumed as we load up the threads, the results look very linear.

This is as we load two threads onto one core at a time. The processor slowly adds power to the cores when threads are assigned.

Comparing to the other two ‘95W’ processors, we can see that the Core i9-9900K pushes more power as more cores are loaded. Despite Intel officially giving all three the same TDP at 95W, and the same PL2 at 210W, there are clear differences due to the fixed turbo tables embedded in each BIOS.

So is TDP Pointless? Yes, But There is a Solution

If you believe that TDP is the peak power draw of the processor under default scenarios, then yes, TDP is pointless, and technically it has been for generations. However under the miasma of a decade of quad core processors, most parts didn’t even reach the TDP rating even under full load – it wasn’t until we started getting higher core count parts, at the same or higher frequency, where it started becoming an issue.

But fear not, there is a solution. Or at least I want to offer one to both Intel and AMD, to see if they will take me up on the offer. The solution here is to offer two TDP ratings: a TDP and a TDP-Peak. In Intel lingo, this is PL1 and PL2, but basically the TDP-Peak takes into account the ‘all-core’ turbo. It doesn’t have to be covered under warranty (because as of right now, turbo is not), but it should be an indication for the nature of the cooling that a user needs to purchase if they want the best performance. Otherwise it’s a case of fumbling in the dark.

Gaming: Integrated Graphics Overclocking
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  • Ryan Smith - Friday, October 19, 2018 - link

    For once, we're going to do the first comment!

    (What does everyone think of the article, and Intel's new CPU?)
    Reply
  • DanNeely - Friday, October 19, 2018 - link

    [thoughts] Reply
  • Ryan Smith - Friday, October 19, 2018 - link

    Okay. That's well-played... Reply
  • nathanddrews - Friday, October 19, 2018 - link

    My take on your data: worth it if you have something a lot faster than a GTX 1080 since it looks GPU-bound for most of the gaming benchmarks at med-high resolutions. 2080Ti users and SLI users will probably get the most out of it from a gaming perspective.

    Skylake-X with that AVX512 perf, though...
    Reply
  • Ian Cutress - Friday, October 19, 2018 - link

    One issue we always have every generation is sourcing GPUs. Going up to a vendor and asking for 3-4 cards is typically a no go. This is why I've done a range of resolutions/settings for each game, so cover everyone who wants to see CPU limited scenarios, and others that might be more real-world oriented. Reply
  • 3dGfx - Friday, October 19, 2018 - link

    Ian, how can you claim 9900k is the best when you never tested the HEDT parts in gaming? Making such claims really makes anandtech look bad because it sounds like a sales pitch and you omitted that entire HEDT platform from the results. I hope you fix this oversight so skyX can be compared properly to 9900K and the upcoming skyX refresh parts! And of course, AMD HEDT parts.

    There was supposed to be a part2 to the i9-7980XE review and it never happened, so gaming benchmarks were never done, and i9-7940X and i9-7920X weren't tested either. HEDT is a gaming platform since it has no ECC support and isn't marketed as a workstation platform.

    IF intel says the 8-core part is now "the best" you ought to be testing their flagship HEDT parts which also were claimed to be the best.
    Reply
  • 3dGfx - Friday, October 19, 2018 - link

    p.s. It would be nice if you can also do Zbrush benchmarking for all the cpu reviews. it runs entirely on the CPU with no GPU accelerations and it comes with a benchmark test/score built into the app. Zbrush is a very common 3d app these days. Also its useful to mention in a review how many polygons or subdivision levels can be displayed in zbrush by the cpu before you see a slowdown. thanks. Reply
  • Ryan Smith - Friday, October 19, 2018 - link

    "Ian, how can you claim 9900k is the best when you never tested the HEDT parts in gaming?"

    Beg your pardon? We have the 7900X, 7820X, and a couple of Threadrippers for good measure. Past that, the farther up the ladder you go in Intel HEDT, the lower the turbo clockspeeds go, which diminishes gaming performance.
    Reply
  • 3dGfx - Friday, October 19, 2018 - link

    sorry, I was mainly just looking for the flagship products and they have no gaming benches at all, 2990WX, 2950X, and 7980XE, these top end "best" parts have no gaming benchmarks. I wanted to see how they compare to the 9900k or to the refreshed skylakeX which will come out. if for example someone wants to buy a chip that is good for both raytrace rendering and games (game developers, etc.) they will want to see all these benches. Reply
  • Makaveli - Friday, October 19, 2018 - link

    Why would you buy a 2990WX, 2950X, and 7980XE

    to play games on?
    Reply

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