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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  • Rocket_Scientist - Friday, July 16, 2021 - link

    I want to know who spends 5 grand on a processor but doesn't spend the few extra dollars to utilize all 8 memory channels! Reply
  • Mikewind Dale - Friday, July 16, 2021 - link

    The 3955WX processor "only" costs $1,150, while each stick of 64 GB RAM costs $350.

    And I wanted to keep some empty slots in case 128 GB RDIMMs became affordable. But I didn't know that using 6 channels would cause so much performance degradation.
    Reply
  • mode_13h - Saturday, July 17, 2021 - link

    > who spends 5 grand on a processor but doesn't spend
    > the few extra dollars to utilize all 8 memory channels!

    Although I tend to agree, the article did reveal some benchmarks where the additional bandwidth provides negligible benefit.
    Reply
  • lmh - Tuesday, July 27, 2021 - link

    Can you share what memory bandwidth you actually measured in the 3955WX 8-channel configuration? Reply
  • McFig - Wednesday, July 14, 2021 - link

    There’s an error in the table “AMD 32-Core Zen 2 Comparison”: The MSRPs are mixed up. Reply
  • McFig - Wednesday, July 14, 2021 - link

    Also: “code bath”; “Undreal” (I’m guessing should be “Unreal”?); “but also the updates” (e.g. could be “but also there were significant updates”) Reply
  • SarahKerrigan - Wednesday, July 14, 2021 - link

    I kind of like "Code Bath." Reply
  • Threska - Wednesday, July 14, 2021 - link

    " This is part of AMD’s guaranteed supply chain process, allowing OEMs to hard lock processors into certain vendors for supply chain end-to-end security that is requested by specific customers."

    I ASSUME that's a feature a certain OS vendor can't access.

    "Only select vendors seem to have access/licenses to make WRX80 motherboards, and your main options are:"

    I've seen the Giga offered as a burn-in special with a bundled processor, making it a better deal. The Asus is nice but I have to wonder if it's worth all the features.
    Reply
  • DesireeTR - Wednesday, July 14, 2021 - link

    No, It's worse. There's article about AMD Platform Secure Boot Feature (PSB) by servethehome together with Dell EMC. It basically burns permanently a public key of the OEM into the EPYC processor. It creates a guarantee that both motherboard and processor are not tampered. If you move your processor from OEM A that enabled PSB to motherboard of OEM B, AMD Secure Processor considers that as tampering and stops it working. The reverse is true.

    Some OEM are very strict (Dell EMC does this by hardware burn-in), some are less strict (HPE use
    Reply
  • DesireeTR - Wednesday, July 14, 2021 - link

    HPE only locks the public key in the firmware, and perform tamper check on BIOS only). And I guess before long, all PRO processor might get the same PSB feature too. Reply

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