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An Early Look At The AMD P-State CPPC Driver Performance vs. ACPI CPUFreq

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  • An Early Look At The AMD P-State CPPC Driver Performance vs. ACPI CPUFreq

    Phoronix: An Early Look At The AMD P-State CPPC Driver Performance vs. ACPI CPUFreq

    Earlier this month AMD posted their initial public patches for the AMD P-State CPU frequency scaling driver that leverages ACPI CPPC for ultimately aiming to provide better power efficiency and more responsive CPU frequency scaling / performance state decisions on Zen 3 (and Zen 2 eventually) processors. This is part of the effort around AMD and Valve collaborating for better Linux efficiency especially with the AMD-powered Steam Deck.

    https://www.phoronix.com/vr.php?view=30535

  • #2
    Note that the platform (e.g., sbios, ACPI) needs to support CPPC for this driver to load regardless of whether the chip is zen2 or zen3. Not all platforms enable CPPC. It's up to the OEM.

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    • #3
      For games? acpi-cpufreq.
      For others applications? amd-pstate.

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      • #4
        Originally posted by agd5f View Post
        Note that the platform (e.g., sbios, ACPI) needs to support CPPC for this driver to load regardless of whether the chip is zen2 or zen3. Not all platforms enable CPPC. It's up to the OEM.
        How can we test if our sbios/acpi supports cpcc? Is there some output logged at dmesg when enabling amd-pstate?

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        • #5
          Originally posted by bezirg View Post

          How can we test if our sbios/acpi supports cpcc? Is there some output logged at dmesg when enabling amd-pstate?
          The amd-pstate driver won't load if the system doesn't support it.

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          • #6
            @michael: duplication in last page: "be as bad as bad as"

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            • #7
              @Michael: You should always consider perf/watt for ondemand as most important figure. Nobody cares if you have 350 or 330 Fps, but if the wattage goes down measurably, that's important.

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              • #8
                Originally posted by bezirg View Post

                How can we test if our sbios/acpi supports cpcc? Is there some output logged at dmesg when enabling amd-pstate?
                When you try to load the module it'll fail with:

                modprobe: ERROR: could not insert 'amd_pstate': No such device
                Running "modprobe amd_pstate dyndbg==pmf" shows me:

                amd_pstate:amd_pstate_init: amd_pstate: amd_pstate_init, the _CPC object is not present in SBIOS

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                • #9
                  What's up with schedutil anyway? Seems to be worse than ondemand for both performance and power consumption?!

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                  • #10
                    Extremely disappointing so far, we need something like goal funding for improving schedutil as a base...

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