A Few Words on Power Consumption

When we tested the first wave of Skylake-X processors, one of the take away points was that Intel was starting to push the blurred line between thermal design power (TDP) and power consumption. Technically the TDP is a value, in Watts, to which a CPU cooler should be designed to cope with heat energy of that amount: a processor with a 140W TDP should be paired with a CPU cooler that can dissipate a minimum of 140W in order to avoid temperature spikes and ‘thermal runaway’. Failure to do so will cause the processor to hit thermal limits and reduce performance to compensate. Normally the TDP is, on average, also a good metric for power consumption values. A processor with a TDP of 140W should, in general, consume 140W of power (plus some efficiency losses).

In the past, particularly with mainstream processors, and even with the latest batch of mainstream processors, Intel typically rides the power consumption well under the rated TDP value. The Core i5-7600K for example has a TDP of 95W, and we measured a power consumption of ~61W, of which ~53W was from the CPU cores. So when we say that in the past Intel has been conservative with the TDP value, this is typically the sort of metric we will quote.

With the initial Skylake-X launch, things were a little different. Due to the high all-core frequencies, the new mesh topology, the advent of AVX-512, and the sheer number of cores in play, the power consumption was matching the TDP and even exceeding it in some cases. The Core i9-7900X is rated at 140W TDP, however we measured 149W, a 6.4% difference. The previous generation 10-core, the Core i7-6950X was also rated at 140W, but only draws 111W at load. Intel’s power strategy has changed with Skylake-X, particularly as we ramp up the number of cores.

Even though we didn’t perform the testing ourselves, our colleagues over at Tom’s Hardware, Paul Alcorn and Igor Wallossek, did extensive power testing on the Skylake-X processors. Along with showing that the power delivery system of the new motherboards works best with substantial heatsinks and active cooling (such as a VRM fan), they showed that with the right overclock, a user can draw over 330W without too much fuss.

So for the two processors in the review today, the same high values ring true. Almost to the point of it being alarmingly so. Both the Core i9-7980XE and the Core i9-7960X have a TDP rating of 165W, and we start with the peak headline numbers first. Our power testing implements a Prime95 stress test, with the data taken from the internal power management registers that the hardware uses to manage power delivery and frequency response. This method is not as accurate as a physical measurement, but is more universal, it removes the need to tool up every single product, and the hardware itself uses these values to make decisions about the performance response.

Power: Total Package (Full Load)

At full load, the total package power consumption for the Core i9-7960X is almost on the money, drawing 163W.

However the Core i9-7980XE goes above and beyond (and not necessarily in a good way). At full load, running an all-core frequency of 3.4 GHz, we recorded a total package power consumption of 190.36W. This is a 25W increase over the TDP value, or a 15.4% gain. Assuming our singular CPU is ‘representative’, I’d hazard a guess and say that the TDP value of this processor should be nearer 190W, or 205W to be on the safe side. Unfortunately, when Intel started designing the Basin Falls platform, it only was designed to be rated at 165W. This is a case of Intel pushing the margins, perhaps a little too far for some. It will be interesting to get the Xeon-W processors in for equivalent testing.

Our power testing program can also pull out a breakdown of the power consumption, depending if the registers are preconfigured in the software. In this case we were also able to pull out values for the DRAM controller(s) power consumption, although looking at the values this is likely to include the uncore/mesh as well. For both CPUs at load, we see that this DRAM and mesh combination is drawing ~42W. If we remove this from the load power numbers, that leaves 121W for the 16-core chip (7.5W per core) and 140W for the 18-core chip (7.8W per core).

Power: Cores Only (Full Load)

Most of the rise of the power consumption, for both the cores and DRAM, happens when the processor is loaded to four threads - the Core i9-7980XE is drawing 100W+ when four threads are loaded. This is what we expect to see: when the processor is lightly loaded and in turbo mode, a core can consume upwards of 20W, while at load it will migrate down to a smaller value. We saw the same with with Ryzen, drawing 17W per core when lightly threaded down to 6W per core when loaded. Obviously the peak efficiency point for these cores is down nearer the 6-8W range than up at the 15-20W range.

Unfortunately, due to timing, we did not perform any overclocking to see the effect it has on power. There was one number in the review materials we received that will likely be checked with our other Purch colleagues: one motherboard vendor quoted the power consumption of the Core i9-7980XE, when overclocked to 4.4 GHz, will reach over 500W. I think someone wants IBM’s record. It also means that the choice of CPU cooler is an important factor in all of this: very few off-the-shelf solutions will happily deal with 300W properly, let alone 500W. These processors are unlikely to bring about a boom in custom liquid cooling loops, however for the professionals that want all the cores and also peak single thread performance, start looking at pre-built overclocked systems that emphasize a massive amount of cooling capability.

A Quick Run on Efficiency

Some of our readers have requested a look into some efficiency numbers. We’re still in the process of producing a good way to represent this data, and take power numbers directly during the benchmark to get a full accurate reading. In the meantime, we’re going to take a benchmark we know hammers every thread of every CPU and put that against our load power readings.

First up is Corona. We take the benchmark result and divide by the load power, to get the efficiency value. This value is then reduced by a constant factor to provide a single digit number.

In a rendering task like Corona, where all the threads are hammered all the time, both the Skylake-X parts out-perform Threadripper for power efficiency, although not by twice as much. Interestingly the results show that as we reduce the clocks on TR, the 1700 comes out on top for pure efficiency in this test.

HandBrake’s HEVC efficiency with large frames actually peaks with the Core i5 here, with the 1700 not far behind. All the Skylake-X processors out-perform Threadripper on efficiency.

Benchmarking Performance: CPU Legacy Tests Performance Per Dollar Analysis


View All Comments

  • mapesdhs - Monday, September 25, 2017 - link

    Just curious mmrezaie, why do you say "unofficially"? ECC support is included on specs pages for X399 boards. Reply
  • frowertr - Tuesday, September 26, 2017 - link

    Run Unbound on a Pi or other Linux VM and block all thise adverts at the DNS level for all the devices on your LAN. I havent seen a site add anywhere in years from my home. Reply
  • Notmyusualid - Thursday, September 28, 2017 - link


    Interesting - But that won't work for me - I'm a frequent traveller, and thus on different LANs all the time.

    But what works for me, is PeerBlock, then iblocklist.com for the Ad-server & Malicious lists and others, add Microsoft and any other entity I don't want my packets broadcast to (my Antivirus alerts me when I need updates anyway - and thus I temporarily allow http through the firewall for that type of occasion).
  • realistz - Monday, September 25, 2017 - link

    This is why the "core wars" won't be a good thing for consumers. Focus on better single thread perf instead quantity. Reply
  • sonichedgehog360@yahoo.com - Monday, September 25, 2017 - link

    On the contrary, single-threaded performance is largely a dead end until we hit quantum computing due to instability inherent to extremely high clock speeds. The core wars is exactly what we need to incentivize developers to improve multi-core scaling and performance: it represents the future of computing. Reply
  • extide - Monday, September 25, 2017 - link

    Some things just can't be split up into multiple threads -- it's not a developer skill level or laziness issue, it's just the way it is. Single threaded speed will always be important. Reply
  • PixyMisa - Monday, September 25, 2017 - link

    Maybe, but it's still a dead end. It's not going to improve much, ever. Reply
  • HStewart - Monday, September 25, 2017 - link

    As a developer for 30 years this is absolutely correct - especially with the user interface logic which includes graphics. Until technology is a truly able to multi-thread the display logic and display hardware - it very important to have single thread performance. I would think this is critically important for games since they deal a lot with screen. Intel has also done something very wise and I believe they realize this important - by allowing some cores to go faster than others. Multi-core is basically hardware assisted multi-threaded applications which is very dependent on application design - most of time threads are used for background tasks. Another critical error is database logic - unless the database core logic is designed to be multithread, you will need single point of entry and in some cases - they database must be on screen thread. Of course with advancement is possible hardware to handle threading and such, it might be possible to over come these limitations. But in NO WAY this is laziness of developer - keep in mind a lot of software has years of development and to completely rewrite the technology is a major and costly effort. Reply
  • lilmoe - Monday, September 25, 2017 - link

    There are lots of instances where I'd need summation and other complex algorithm results from millions of records in certain tables. If I'm going the traditional sql route, it would take ages for the computation to return the desired values. I instead divide the load one multiple threads to get a smaller set in which I would perform some cleanup and final arithmetic. Lots of extra work? Yup. More ram per transaction total? Oh yea. Faster? Yes, dramatically faster.

    WPF was the first attempt by Microsoft to distribute UI load across multiple cores in addition to the gpu, it was so slow in its early days due to lots out inefficiencies and premature multi-core hardware. It's alot better now, but much more work than WinForms as you'd guess. UWP UI is also completely multithreaded.

    Android is inching closer to completely have it's UI multithreaded and separate from the main worker thread. We're getting there.

    Both you and sonich are correct, but it's also a fact that developers are taking their sweet time to get familiar with and/or use these technologies. Some don't want to that route simply because of technology bias and lock-in.
  • HStewart - Monday, September 25, 2017 - link

    "Both you and sonich are correct, but it's also a fact that developers are taking their sweet time to get familiar with and/or use these technologies. Some don't want to that route simply because of technology bias and lock-in."

    That is not exactly what I was saying - it completely understandable to use threads to handle calculation - but I am saying that the designed of hardware with a single screen element makes it hard for true multi-threading. Often the critical sections must be lock - especially in a multi-processor system.

    The best use of multi-threading and mult-cpu systems is actually in 3D rendering, this is where multiple threads can be use to distribute the load. In been a while since I work with Lightwave 3D and Vue, but in those days I would create a render farm - one of reason, I purchase a Dual Xeon 5160 ten years ago. But now a days processors like these processors here could do the work or 10 or normal machines on my farm ( Xeon was significantly more power then the P4's - pretty much could do the work of 4 or more P4's back then )

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