Commit 0005a190 authored by Bastien Nocera's avatar Bastien Nocera
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...@@ -101,13 +101,14 @@ Operations on Intel-based machines ...@@ -101,13 +101,14 @@ Operations on Intel-based machines
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The "driver" for making the hardware act on the user-selected power profile on Intel 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 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 CPU supports either hardware-managed P-states (HWP) or Energy Performance Bias (EPB).
scaling driver is set to `passive` mode.
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
cat: /sys/firmware/acpi/platform_profile_choices: No such file or directory cat: /sys/firmware/acpi/platform_profile_choices: No such file or directory
...@@ -115,16 +116,23 @@ $ cat /sys/devices/system/cpu/intel_pstate/status ...@@ -115,16 +116,23 @@ $ cat /sys/devices/system/cpu/intel_pstate/status
active 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 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 support HWP, or the administator has disabled it, and `EPB` isn't available, then the
used, and there won't be a performance mode. 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 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 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, 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 Testing
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