Power Consumption

The nature of reporting processor power consumption has become, in part, a dystopian nightmare. Historically the peak power consumption of a processor, as purchased, is given by its Thermal Design Power (TDP, or PL1). For many markets, such as embedded processors, that value of TDP still signifies the peak power consumption. For the processors we test at AnandTech, either desktop, notebook, or enterprise, this is not always the case.

Modern high performance processors implement a feature called Turbo. This allows, usually for a limited time, a processor to go beyond its rated frequency. Exactly how far the processor goes depends on a few factors, such as the Turbo Power Limit (PL2), whether the peak frequency is hard coded, the thermals, and the power delivery. Turbo can sometimes be very aggressive, allowing power values 2.5x above the rated TDP.

AMD and Intel have different definitions for TDP, but are broadly speaking applied the same. The difference comes to turbo modes, turbo limits, turbo budgets, and how the processors manage that power balance. These topics are 10000-12000 word articles in their own right, and we’ve got a few articles worth reading on the topic.

In simple terms, processor manufacturers only ever guarantee two values which are tied together - when all cores are running at base frequency, the processor should be running at or below the TDP rating. All turbo modes and power modes above that are not covered by warranty. Intel kind of screwed this up with the Tiger Lake launch in September 2020, by refusing to define a TDP rating for its new processors, instead going for a range. Obfuscation like this is a frustrating endeavor for press and end-users alike.

However, for our tests in this review, we measure the power consumption of the processor in a variety of different scenarios. These include full peak AVX workflows, a loaded rendered test, and others as appropriate. These tests are done as comparative models. We also note the peak power recorded in any of our tests.

First up is our loaded rendered test, designed to peak out at max power.

In this test the 3995WX with only 64 threads actually uses slightly less power, given that one thread per core doesn’t keep everything active. Despite this, the 64C/64T benchmark result is ~16000 points, compared to ~12600 points when all 128 threads are enabled. Also in this chart we see that the 3955WX with only sixteen cores hovers around the 212W mark.

The second test is from y-Cruncher, which is our AVX2/AVX512 workload. This also has some memory requirements, which can lead to periodic cycling with systems that have lower memory bandwidth per core options.

Both of the 3995WX configurations perform similarly, while the 3975WX has more variability as it requests data from memory causing the cores to idle slightly. The 3955WX peaks around 250W this time.

For peak power, we report the highest value observed from any of our benchmark tests.

(0-0) Peak Power

As with most AMD processors, there is a total package power tracking value, and for Threadripper Pro that is the same as the TDP at 280 W. I have included the AVX2 values here for the Intel processors, however at AVX512 these will turbo to 296 W (i9-11900K) and 291 W (W-3175X).

AMD TR Pro Review: 3995WX, 3975WX, 3955WX CPU Tests: Rendering
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  • Spunjji - Friday, July 16, 2021 - link

    Having seen how modern processors behave with insufficient cooling, Threska's right that it won't get "fried", but you're correct to infer that it would result in unpredictably sub-optimal performance.

    Anecdotally, I had a friend with a Sandy Bridge system with a cooling issue that he only noticed when he bought a new GPU and ran 3DMark and got unexpectedly low results. The "cooling issue" was that the stock heatsink wasn't even making contact with the CPU heat-spreader; he'd been gaming with the system for 3 years by that point. 😬
  • serpretetsky - Friday, July 16, 2021 - link

    I had to do some thermal shutdown testing on some consumer intel cpu. I forgot which one. Maybe i5/i7 8000 series?

    With server CPUs this was usually pretty easy, remove fan, and wait for shutdown. With the consumer CPU it kept running. So i completely removed the heatsink, the thing simply downclocked to 800 MHz, and continued running happily with no heatsink. Booted to linux, ran everything great, and no heatsink (actually once it booted to linux I think it even started clocking back up once in a while). I had get a hot-air soldering gun to heat it up till shutdown.
  • mode_13h - Saturday, July 17, 2021 - link

    5-10 years ago, there was a heatsink gasket where you have to get near 100 degrees C to melt the material so it fuses with the heatsink and CPU. I forget the name, but I'm wondering if it's even possible to do that any more.
  • skaurus - Wednesday, July 14, 2021 - link

    That's great analysis.
  • Threska - Wednesday, July 14, 2021 - link

    It would be nice to see how these MBs do with VFIO since that has considerations most users don't.
  • mode_13h - Wednesday, July 14, 2021 - link

    Ian, is the source code for your 3DPM benchmark published anywhere? If not, it would be nice if we could see it and compare the AVX2 path with the AVX-512 one. Also, maybe someone could add support for ARM NEON or SVE.
  • techguymaxc - Wednesday, July 14, 2021 - link

    I'm slightly confused by the concluding remarks.

    "Performance between Threadripper Pro and Threadripper came in three stages. Either (a) the results between similar processors was practically identical, (b) Threadripper beat TR Pro by a small margin due to slightly higher frequencies, or (c) TR Pro thrashed Threadripper due to memory bandwidth availability. That last point, (c), only really kicks in for the 32c and 64c processors it should be noted. Our 16c TR Pro had the same memory bandwidth results as TR, most likely due to only having two chiplets in its design."

    A and B are observable, but C only proves true in synthetic benchmarks (and Pi calculation). Is there a real-world use-case for the additional memory bandwidth, outside of calculating Pi?
  • Blastdoor - Wednesday, July 14, 2021 - link

    The advantage shows up with multi-threaded SPEC. SPEC is essentially a composite of a suite of real-world tasks. I guess you could call it 'synthetic' due to it being a composite, but the individual tasks don't strike me as 'synthetic.' For example, here's a description of namd: https://www.spec.org/cpu2017/Docs/benchmarks/508.n...
  • techguymaxc - Wednesday, July 14, 2021 - link

    Thanks for that info. It would be nice to see the breakdown of individual test results from the SPEC suite.
  • arashi - Saturday, July 17, 2021 - link


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