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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  • GreenReaper - Friday, October 19, 2018 - link

    The answer is "yes, with a but". Certain things scale really well with hyperthreading. Other things can see a severe regression, as it thrashes between one workload and another and/or overheats the CPU, reducing its ability to boost.

    Cache contention can be an issue: the i9-9900K has only 33% more cache than the i7-9700K, not 100% (and even if there were, it wouldn't have the same behaviour unless it was strictly partitioned). Memory bandwidth contention is a thing, too. And within the CPU, some parts can not be partitioned - it just relies on them running fast enough to supplky the parts which can.

    And clearly hyperthreading has an impact on overclocking ability. It might be interesting to see the gaming graphs with the i7-9700K@5.3Ghz vs. i9-9900K@5.0Ghz (or, if you want to save 50W, i7-9700K@5.0Ghz vs. i9-9900K@4.7Ghz - basically the i9-9900K's default all-core boost, but 400Mhz above the i7-9700K's 4.6Ghz all-core default, both for the same power).
    Reply
  • NaterGator - Friday, October 19, 2018 - link

    Any chance y'all would be willing to run those HT-bound tests with the 9900K's HT disabled in the BIOS? Reply
  • ekidhardt - Friday, October 19, 2018 - link

    Thanks for the review!

    I think far too much emphasis has been placed on 'value'. I simply want the fastest, most powerful CPU that isn't priced absurdly high.

    While the 9900k msrp is high, it's not in the realm of irrational spending, it's a few hundred dollars more. For a person that upgrades once every 5-6 years--a few hundred extra is not that important to me.

    I'd also like to argue against those protesting pre-order logic. I pre-ordered. And my logic is this: intel has a CLEAR track record of great CPU's. There hasn't been any surprisingly terrible CPU's released. They're consistently reliable.

    Anyway! I'm happy I pre-ordered and don't care that it costs a little bit extra; I've got a fast 8 core 16 thread CPU that should last quite a while.
    Reply
  • Schmich - Friday, October 19, 2018 - link

    You have the numbers anyway. Not everyone buys the highest end and then wait many years to upgrade. That isn't the smartest choice because you spend so much money and then after 2-3 years you're just a mid-ranger.

    For those who want high-end they can still get a 2700x today, and then the 3700x next year with most likely better performance than your 9900k due to 7nm, PLUS have money over PLUS a spare 2700x they can sell.

    Same thing for GPU except for this gen. I never understood those who buy the xx80Ti version and then upgrade after 5 years. Your overall experience would be better only getting the xx70 but upgrading more often.
    Reply
  • Spunjji - Monday, October 22, 2018 - link

    This is what actual logic looks like! Reply
  • Gastec - Sunday, November 04, 2018 - link

    Basically "The more you buy, the more you save" :-\ Reply
  • shaolin95 - Friday, October 19, 2018 - link

    Exactly. I think the ones beating the value dead horse are mainly AMD fanboys defending their 2700x purchase Reply
  • eva02langley - Friday, October 19, 2018 - link

    Sorry, value is a huge aspect. The reason why RTX is such an issue. Also, at this price point, I would go HEDT if compute was really that important for me.

    It is not with 10-15% performance increase over a 2700x at 1080p with a damn 1080 TI that I will see a justified purchase.
    Reply
  • Arbie - Friday, October 19, 2018 - link

    Gratuitous trolling, drags down thread quality. Do you really still need to be told what AMD has done for this market? Do you even think this product would exist without them - except at maybe twice the already high price? Go pick on someone that deserves your scorn, such as ... Intel. Reply
  • Great_Scott - Friday, October 19, 2018 - link

    What a mess. I guess gaming really doesn't depend on the CPU any more. Those Ryzen machines were running at a 1Ghz+ speed deficit and still do decently.

    Intel needs a new core design and AMD needs a new fab.
    Reply

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