Control Windows 10's "Power Mode" programmatically

Question

Background

Hi. I have an SB2 (Surface Book 2), and I'm one of the unlucky users who are facing the infamous 0.4GHz throttling problem that is plaguing many of the SB2 machines. The problem is that the SB2 suddenly, and very frequently depending on the ambient temperature, throttles heavily from a boost of 4GHz to 0.4GHz and hangs in there for a minute or two (this causes a severe slow-down of the whole laptop). This is extremely frustrating and almost makes the machine unusable for even the simplest of workloads.

Microsoft apparently stated that it fixed the problem in the October 2019 update, but I and several other users are still facing it. I'm very positive my machine is up to date, and I even manually installed all the latest Surface Book 2 firmware updates.

Here's a capture of the CPU state when the problem is happening:

As you can see, the temperature of the unit itself isn't high at all, but CPU is throttling at 0.4GHz exactly.

More links about this: 1 2

Workarounds

I tried pretty much EVERYTHING. Undervolting until freezing screens, disabling BD PROCHOT, disabling power throttling in GPE, messing up with the registry, tuning several CPU/GPU settings. Nothing worked.

You can do only 2 things when the throttling starts:

1. Wait for it to finish (usually takes a minute or two).
2. Change the Power Mode in windows 10. It doesn't even matter if you're changing it from "Best performance" to "Best battery life", what matters is that you change it. As soon as you do, throttling completely stops in a couple seconds. This is the only manual solution that worked.

Question

In practice, changing this slider each 10 seconds no matter how heavy the workload is, indefinitely lead to a smooth experience without throttling. Of course, this isn't a feasible workaround by hand.

In theory, I thought that if I could find a way to control this mode programmatically, I might be able to wish this problem goodbye by switching power modes every 10 seconds or so.

I don't mind if it's in win32 (winapi) or a .net thing. I looked a lot, found this about power management, but it seems there's no interface for setting in win32. I could have overlooked it, so here's my question:

Is there any way at all to control the Power Mode in Windows 10 programmatically?

Answer 1

OK... I've been wanting command line or programmatic access to adjust the power slider for a while, and I've run across this post multiple times when looking into it. I'm surprised no one else has bothered to figure it out. I worked it out myself today, motivated by the fact that Windows 11 appears to have removed the power slider from the taskbar and you have to go digging into the Settings app to adjust it.

As previously discussed, in the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power\User\PowerSchemes you can find values "ActiveOverlayAcPowerScheme" and "ActiveOverlayDcPowerScheme" which record the current values of the slider for AC power and battery power, respectively. However, changing these values is not sufficient to adjust the power slider or the system's mode of operation.

Turns out there is an undocumented method in C:\Windows\System32\powrprof.dll called PowerSetActiveOverlayScheme. It takes a single parameter. I "guessed" that it would take a GUID in the same manner that PowerSetActiveScheme does, and it seems to work.

Note — Using an undocumented API is unsupported by Microsoft. This method may break in future Windows releases. It can be used for personal tinkering but I would not suggest using it in any actual production projects.

Here is the C# PInvoke signature:

[DllImportAttribute("powrprof.dll", EntryPoint = "PowerSetActiveOverlayScheme")]
public static extern uint PowerSetActiveOverlayScheme(Guid OverlaySchemeGuid);

It returns zero on success and non-zero on failure.

Calling it is as simple as:

PowerSetActiveOverlayScheme(new Guid("ded574b5-45a0-4f42-8737-46345c09c238"));

It has immediate effect. This particular GUID moved the slider all the way to the right for me and also updated the "ActiveOverlayAcPowerScheme" value in the registry. Using a GUID of all zeros reset the slider to the middle value. You can see what GUID options are available by just observing the values that show up in the registry when you set the power slider to different positions.

There are two methods that can be used to read the current position of the slider. I'm not sure what the difference between them is, they returned the same value each time in my testing.

[DllImportAttribute("powrprof.dll", EntryPoint = "PowerGetActualOverlayScheme")]
public static extern uint PowerGetActualOverlayScheme(out Guid ActualOverlayGuid);

[DllImportAttribute("powrprof.dll", EntryPoint = "PowerGetEffectiveOverlayScheme")]
public static extern uint PowerGetEffectiveOverlayScheme(out Guid EffectiveOverlayGuid);

They also return zero on success and non-zero on failure. They can be called like...

if (PowerGetEffectiveOverlayScheme(out Guid activeScheme) == 0)
{
    Console.WriteLine(activeScheme);
}

There is one more method called "PowerGetOverlaySchemes", which I presume can be used to fetch a list of available GUIDs that could be used. It appears to take three parameters and I haven't bothered with figuring it out.

I created a command-line program which can be used to set the power mode, and it can be found at https://github.com/AaronKelley/PowerMode.