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    Intel-undervolt: CPU undervolting and throttling configuration tool for Linux

    (github.com)
    132 points cl3misch | 11 comments | 17 Jun 24 22:44 UTC | HN request time: 0.207s | source | bottom
    1. hu3 ◴[18 Jun 24 14:26 UTC] No.40718245[source]▶
    I slightly undervolted an i7 11800H by -100mV.

    That resulted in a -10C average CPU temperature. Massive!

    I don't remember last time I heard the fans. Not even with Docker + Jetbrains IDEs.

    I wonder why doesn't it come like this by default. It runs faster too because it's no longer frequently thermal throttled.

    replies(4): >>40718594 #>>40718806 #>>40719032 #>>40733881 #
    2. atVelocet ◴[18 Jun 24 15:00 UTC] No.40718594[source]▶
    Cause the CPU can get unstable under certain loads. So Intel plays it safe and ramps up the voltage. And no.. there is no easy way to measure this. Also every CPU is slightly different.
    replies(2): >>40718698 #>>40718737 #
    3. StrangeDoctor ◴[18 Jun 24 15:10 UTC] No.40718698[source]▶
    I ultimately gave up playing this game, spent hours testing and tuning. Each core is slightly different (on amd, I’m sure intel has something similar) and stress test for 1-24h each tweak invoking a reboot. Then some new workload comes and kernel panic/bsod.

    Stock settings just work, maybe I lost the silicon lottery but too tired to check anymore.

    4. rcthompson ◴[18 Jun 24 15:13 UTC] No.40718737[source]▶
    It's not just unstable, it's a security issue because control over CPU voltage allows someone to use that instability to compromise computations that are supposed to be performed securely (e.g. look up "Plundervolt").
    replies(1): >>40722131 #
    5. Out_of_Characte ◴[18 Jun 24 15:19 UTC] No.40718806[source]▶
    Because not all chips will be stable at -100mV Intel is providing the chip with warranty/guarantee that the chip performs 'up to' spec.

    Is your chip completely stable in all workloads? Would it be stable at 90c? when all Dram slots are occupied? When driving all pcie lanes at max?

    I bet that you could make any chip unstable with the right tools and knowledge.

    replies(1): >>40718960 #
    6. hu3 ◴[18 Jun 24 15:30 UTC] No.40718960[source]▶
    At the time, I ran a CPU stress test which put all cores at full load for a couple of hours.

    Then I ran RAM tests.

    Then I ran NVMe stress tests.

    Then I ran GPU stress tests (NVIDIA GPU is underclocked).

    Then I ran all of these tests together.

    Worked butter smooth. Not a crash to this day.

    To be fair, -100mV is on the safe side according to the articles I read at the time. Some folks run at -200mV or less. I don't need that kind of tweak.

    replies(2): >>40720377 #>>40743323 #
    7. throwup238 ◴[18 Jun 24 15:34 UTC] No.40719032[source]▶
    > I wonder why doesn't it come like this by default. It runs faster too because it's no longer frequently thermal throttled.

    Because pumping up the voltage also allows them to increase the base clock frequency without causing instability. Consumers learned to compare the frequencies during the CPU wars so that's what they juice for marketing purposes.

    Newer Thinkpads are notorious for this. Many of them can operate fanless 99% of the time if they just undervolted them by 100mV like you did. It's the first thing I do with a new laptop after installing a clean OS.

    8. thot_experiment ◴[18 Jun 24 17:52 UTC] No.40720377{3}[source]▶
    chips do increasingly come like that as intel gets better at binning, they don't want to leave money on the table and are creating more SKUs in order to mark up good chips like yours (this is why silicon lottery is no longer in business)

    the reason your chip didn't come like that is because intel plays it very safe when it comes to stability and their margins for error are likely broader than yours, the stochastic nature of the failures means that the voltage margin between one crash for every 2 hours of stress test and one crash for every day of stress test can be hundreds of milivolts, but they're definitely working on it because pat doesn't want you getting free real estate

    9. epcoa ◴[18 Jun 24 20:55 UTC] No.40722131{3}[source]▶
    If plundervolt is a viable attack you’ve got much bigger problems (the attacker must already have gained full privileges). Not sure how this is relevant to just using throttled or similar to conditionally undervolt the CPU with fixed levels that can be proven reasonably stable.
    10. sausagefeet ◴[20 Jun 24 01:00 UTC] No.40733881[source]▶
    Can undervolting damage hardware? Or do you just reboot and revert settings and go about your day?
    11. RealStickman_ ◴[20 Jun 24 21:01 UTC] No.40743323{3}[source]▶
    When undervolting with an offset, most of the crashes I had were when the CPU state changed. Opening a browser and playing a video from idle, starting a transcode, stuff like that.

    The only way to test is, unfortunately, to use it until it crashes.