On 2021/11/03 16:46, Damien Miller wrote: > On Tue, 2 Nov 2021, Theo de Raadt wrote: > > > Paul de Weerd <we...@weirdnet.nl> wrote: > > > > > A recent commit by Theo changed the hw.perfpolicy behavior to always > > > run at full speed when AC power is on. This means that my workstation > > > (and servers, once I upgrade them) now consumes significantly more > > > power, even though they usually idle. > > > > Did you measure how much more power? > > > > You must measure, to make such a claim. > > > > Your OptiPlex 9020 is probably a modern i5/i7, which probably contains > > C states similar to this: > > > > acpicpu0 at acpi0: C2(200@148 mwait.1@0x33), C1(1000@1 mwait.1), PSS > > > > Which means when the idle loop calls the "mwait" instruction, the cpu > > will 'instantly' slow down to a lower clock and make other power use > > reductions, until an interrupt happens and requires labour again. > > See also https://en.wikichip.org/wiki/race-to-sleep - it's generally > more energy efficient to run the CPU at full speed so it can finish its > work faster and get back to a low-power state sooner
So there's not really any point in doing this scaling on laptops either then, and it could be counterproductive? Would it actually be better for the decision to be "has mwait or an alternative mechanism on other arches" and only if that's absent consider whether it has ac power?
