Windows 7,8,10: are you aware of power plans, their settings and hidden settings

[Maks.K]

Hi guys.

 

I suspect that most of Windows users aware of three power plans utilized in Windows - "High performance", "Balanced" and "Power saver". And OEM installations usually have a custom made power plan from that OEM (especially on notebooks).

Also I suspect that not so much of users ever launched the window with advanced power plan settings.

Finally I am sure even less do know that each power plan has plenty of hidden settings. Those hidden settings could be unhidden so that they will appear in advanced settings window.

 

Most useful among hidden settings are ones related to CPU P-states and C-states.

 

 

In short P-state (performance state) is a pair of values - voltage and frequency - to which CPU can switch. Each modern CPU supports several p-states (where P0 is most powerful, P1 is less powerful than P1, and so forth). Technology is called SpeedStep by Intel and  PowerNow! or Cool'n'Quiet by AMD,

 

C-state (processor state) is an idle/sleep state:

- C0 is fully operational state;

- C1 (often known as Halt) is a state where the processor is not executing instructions (can return to fully operational state essentially instantaneously);

- C2 (often known as Stop-Clock) is a state where the processor maintains all software-visible state but can stop some parts inside (may take longer to wake up);

- C3 (often known as Sleep) is a state where the processor does not need to maintain all software-visible state and can stop and power down more parts inside (longest time to wake up). 

 

P-states, C-states power plan settings I am talking about define the way CPU reacts to increasing and decreasing payload. There are two treshold values for P-states - % of CPU load to switch into higher P-state and into lower P-state. And there are two treshold values for C-states - % of CPU idle to switch CPU into deeper C-state state and into lighter C-state.

 

There two additional settings for P-states - policy for switching to higher P-states and policy for switching to lower P-states.

 

 

Users with Windows 7 and quad (or more) core CPUs should be aware that by default Win7 on "Balanced" and "Power saver" power plans utilizes so called CPU core parking. CPU core parking is just a feature of OS kernel which tries to decrease the amount of working threads executed on the core to be able to switch that core into deeper idle state (more 'sleepy' C-state). User can see all CPU cores targeted for parking - launch Task manager (Ctrl-Shift-Esc), on the tab 'Performance' click 'Open Resource Monitor' link - in Resource monitor switch to tab CPU, there is a pane on the right with all CPU cores usage charts - if you see word 'parked' in the chart title then core is parked. And you can guess that this core parking can be switched off through hidden power plan setting.

 

Why is this relevant? Because with these settings at hands user can configure power plans to his preference. I.e. more flexibility.

For example:

* Even on "High performance" power plan C-states are still in effect. On desktop systems C-states can be disabled in BIOS - but this way you disable them completely while I prefer to have them Off only for "High performance" power plan. And most notebooks do not allow to configure C-states in BIOS.

* "Balanced" power plan has too conservative settings for C-states and P-states by default. I prefer to have this power plan as "Performance on demand" - i.e. CPU increases its performance faster when it is needed and falls back to 'sleep' when payload is ended. 

* "Power saver" power plan can be adjusted to save even more power.

 

If you guys are interested I will show how to unhide these settings and will give example of "performance on demand " values.

 

Forgot to mention that Windows 10 supports new performance management implemented in Intel SkyLake+ CPUs - so called autonomous mode. And the settings in effect are namely hidden power plan settings.

[HarukaNanase]

Good post.

[Maks.K]

Good post.

 

Thanks. Seems like no one is geek/nerd enough, though.