INTEL --

While the Intel Extreme Tuning Utility (XTU) on Windows allows for undervolting laptop processors, currently on Linux there isn’t any Intel-endorsed way for undervolting your CPU should you be interested in better thermal/power efficiency and other factors. But a hypothetical Linux kernel driver could be coming for filling such void.

There does exist the intel-undervolt program that is unofficial and developed by an independent developer for undervolting Intel CPUs from Haswell and newer on Linux. Besides dropping the CPU voltage, it also allows manipulating the throttling power/thermal limits for Intel processors. That intel-undervolt functionality relies on reverse-engineering and discoveries made by the community for the support. That program in turn is touching the CPU MSRs directly for manipulating the behavior.

Jason Donenfeld who is known for his WireGuard work happened to send a patch to kernel developers so writes to the particular OC mailbox MSR won’t result in kernel warnings being printed, the particular MSR used by intel-undervolt. This patch stems from the recent work on Linux aiming to tighten up access to CPU MSRs from user-space.

The discussion among kernel developers to this patch then evolved into whether touching this undocumented MSR should be permitted and in what scenarios, among other concerns. Ultimately though most developers seem in agreement that it would be better for a kernel driver to handle the Intel CPU undervolting than a program running in user-space that is directly interacting with the MSR in question. From there Intel Linux developers also got roped in over the lack of MSR documentation concerning under-volting and any guidance from Intel about any sane manner for supporting such functionality under Linux similar to Intel XTU on Windows.

While there are kernel developers from multiple organizations interested in such functionality for in turn providing an Intel under-volt kernel driver, at the moment the ball appears to be in Intel’s court. There is a need for documentation concerning the relevant MSR(s) and thus waiting on Intel engineers to find such documentation internally and see if/what can be publicly released. Hopefully Intel’s large open-source team will be able to provide some fruits soon as there are many Linux laptop users especially who would enjoy a supported means of easily under-volting their hardware on Linux especially with more vendors beginning to offer pre-loaded Linux laptops.

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  1. Undervolting can work WONDERS. Especially if you get lucky with binning. I'm running the i7 in my little 13" convertible with a ~140mV undervolt, which is the difference between unplayable and 90 pegged in DCS and War Thunder (flight sims) in VR (w/ eGPU). It's also almost an extra hour of battery life when I'm just browsing the internet or whatnot.

  2. > There is a need for documentation concerning the relevant MSR(s) and thus waiting on Intel engineers to find such documentation internally and see if/what can be publicly released. Hopefully Intel's large open-source team will be able to provide some fruits soon

    Well, i915 is certainly a completely different story than nouveau. Otherwise I would not be so optimistic. From the anecdotal evidence of listening to less than a handful of Intel colleagues I happen to have my hopes are not that high. According to them Intel is a horrible organization where high walls and secrecy making is more common than helping another part of the organization.

  3. Do people who like to play with the voltage and clock speed settings of their CPU/GPU/memory typically do so with one of these utilities? Or in the EFI/BIOS config pages?

    I've never done this, but lately it sounds like there's sometimes quite a lot left on the table, even after part binning. Performance is so high now that I wouldn't bother doing this for an extra 5-10%, but for an extra hour of battery life, it's certainly tempting…

  4. In somewhat related news, they just pulled undervolting on XTU for some people recently.

    Speculation being that it was just non-K cpu owners.

    🙁

  5. I think undervolting is good for the environment to lower the carbon footprint of CPUs. Some never multicore CPUs has TDP of +100W, it would probably be much better if we lowered the voltage and frequency for a small CPU performance hit. Thankful to the developers of the driver!

    "The dynamic power consumed by a CPU is approximately proportional to the CPU frequency, and to the square of the CPU voltage:"
    https://en.wikipedia.org/wiki/CPU_power_dissipation

    ps. You can also undervolt, lower frequency of AMD CPUs.

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