Experiments with CPU perf counters and device drivers

Sample code to allow reading and writing of Intel CPU performance registers.

This code takes inspiration from a number of sources, but mainly:

The Intel Systems Programming Guide, Chapter 18 & 19 ("Performance Monitoring" and "Performance Monitoring Events").
Agner Fog's optimization resources, mainly the TestP package (https://www.agner.org/optimize/#testp)
The Windows Driver Samples, mainly https://github.com/microsoft/Windows-driver-samples/tree/master/general/ioctl/wdm

Code layout

There are 3 distinct pieces of code in this repository:

setcr4: A kernel driver which configures the CPU CR4 register to enable user-mode code to read/write the performance counter registers.
runsvc: A user-mode process to load the above driver, and set the CPU flags.
testapp: A sample program that uses the CPU perf counters enabled above.

Building

Ensure the Visual Studio C++ tool-set and the Windows DDK are installed. Then open a 64-bit developer command prompt and run build.bat from the root of the repo.

Notes

By default, an unsigned driver cannot be loaded on Windows 10. Press F8 when booting the OS and select to disable driver signature verification. (Alternately, attach a kernel debugger to the system under test, which also disables it).

Usage

Copy the 3 binary files to C:\temp
Open an Admin command prompt and change the current directory to C:\temp
Run the runsvc.exe utility, which should indicate the driver was loaded.
Press e to enable the Performance Counter Registers (PCRs). (The CR4 register value should change from 0x370678 to 0x370778).
Run the code to test, which now should be able to make use of the counters.
When done, disable the PCRs and unload the driver (press 'd' then 'x' in runsvc.exe).

TODO