diff --git a/README.md b/README.md index 8684372..1093b19 100644 --- a/README.md +++ b/README.md @@ -101,13 +101,14 @@ Operations on Intel-based machines ---------------------------------- The "driver" for making the hardware act on the user-selected power profile on Intel -CPU-based machines is based on the [Intel P-State scaling driver](https://www.kernel.org/doc/html/v5.17/admin-guide/pm/intel_pstate.html). +CPU-based machines is based on the [Intel P-State scaling driver](https://www.kernel.org/doc/html/v5.17/admin-guide/pm/intel_pstate.html) +or the Energy Performance Bias (EPB) feature if available. It is only used if a `platform_profile` driver isn't available for the system, and the -CPU supports hardware-managed P-states (HWP). If HWP isn't supported, or the P-State -scaling driver is set to `passive` mode. +CPU supports either hardware-managed P-states (HWP) or Energy Performance Bias (EPB). -System without `platform_profile support` but with `active` P-State operation mode: +Example of a system without `platform_profile support` but with `active` P-State +operation mode: ``` $ cat /sys/firmware/acpi/platform_profile_choices cat: /sys/firmware/acpi/platform_profile_choices: No such file or directory @@ -115,16 +116,23 @@ $ cat /sys/devices/system/cpu/intel_pstate/status active ``` +Example of a system with `EPB` support: +``` +$ cat /sys/devices/system/cpu/cpu0/power/energy_perf_bias +0 +``` + If the Intel P-State scaling driver is in `passive` mode, either because the system doesn't -support HWP, or the administator has disabled it, then the placeholder driver will be -used, and there won't be a performance mode. +support HWP, or the administator has disabled it, and `EPB` isn't available, then the +placeholder driver will be used, and there won't be a performance mode. Finally, if the Intel P-State scaling driver is used in `active` mode, the P-State scaling governor will be changed to `powersave` as it is the only P-State scaling governor that allows for the "Energy vs Performance Hints" to be taken into consideration, -ie. the only P-State scaling governor that allows power-profiles-daemon to work. +ie. the only P-State scaling governor that allows HWP to work. -For more information, please refer to the [Intel P-State scaling driver documentation](https://www.kernel.org/doc/html/v5.17/admin-guide/pm/intel_pstate.html). +For more information, please refer to the [Intel P-State scaling driver documentation](https://www.kernel.org/doc/html/v5.17/admin-guide/pm/intel_pstate.html) +and the [Intel Performance and Energy Bias Hint](https://www.kernel.org/doc/html/v5.17/admin-guide/pm/intel_epb.html). Testing -------