Tweak CPU Power Elegantly on Windows

KKOCDKO was watching movie on his laptop, but the fan system came into a start-stop cycle, which made him crazy: fan on > cooling > fan off > heating > fan on...

Go to "Control Panel > Power Options > Advanced Settings > Processor Power Management", set "Minimum processor state" to 0%⁽¹⁾, and the "Maximum processor state" is the point.

Set this value to 99%, you can disable the boosting. To 0%, make the frequency to lowest⁽²⁾. But it is troublesome to change the value by hand every time, so:

Using powercfg

@echo off
echo   [1] High   [2] Medium   [3] Low
choice /c 123 >nul
if "%errorLevel%"=="1" set percent=100
if "%errorLevel%"=="2" set percent=99
if "%errorLevel%"=="3" set percent=0
powercfg /setacvalueindex SCHEME_BALANCED SUB_PROCESSOR PROCTHROTTLEMAX %percent%
powercfg /setdcvalueindex SCHEME_BALANCED SUB_PROCESSOR PROCTHROTTLEMAX %percent%
:: Make changes active
powercfg /s SCHEME_BALANCED
exit

(1) Parameter not showed? or Change Ineffective?

(2) Not the lowest, on my R5-5600U, its 1099 MHz.

But why not Linux? Try cpupower.

Using WinAPI

Refer to the descriptions on MSDN, we could find that there are some WinAPI which could modify the power config. So cpu-rate.cc:

#include <windows.h>

#include <powrprof.h>

int main(int argc, char *argv[]) {
  if (argc == 3)
    Sleep(atoi(argv[2]));
  DWORD percent = atoi(argv[1]);
  GUID guid, *scheme = &guid;
  PowerGetActiveScheme(NULL, &scheme);
  PowerWriteACValueIndex(NULL, scheme, &GUID_PROCESSOR_SETTINGS_SUBGROUP,
                         &GUID_PROCESSOR_THROTTLE_MAXIMUM, percent);
  PowerWriteDCValueIndex(NULL, scheme, &GUID_PROCESSOR_SETTINGS_SUBGROUP,
                         &GUID_PROCESSOR_THROTTLE_MAXIMUM, percent);
  PowerSetActiveScheme(NULL, scheme);
  return 0;
}

Seems much complex than powercfg cli tool? But it's fast! On my laptop, the powercfg took 200+ms to finish its process, but this one took only 19ms. This caused we could use this to modify our own CPU schedule policy. For example, I wrote a batch to compile my algorithm study project:

:: cpu-rate <percent> [delay]
start "" cpu-rate 100
clang++ src\main.cc -o build\main
start "" cpu-rate 0 1000
build\main

Now CPU runs on the maximum frequency only in compile. Without this, the default CPU schedule will jump to high frequency even if you move the cursor.

At this moment, I'm coding on our school library, battery usage in the previous 2 hours is only 14% :-)