CPUID

This is a tool to use the CPUID instruction.

I am using the gcc version : __get_cpuid() rather than using the assembly version.

cpuid instruction

The CPUID instruction can be used to retrieve various information about your CPU, such as its vendor string and model number, the size of internal caches and (more interesting), the list of CPU features supported. We will use it to discuss the features and capacity of CPUs for PC states.

You can check if your CPU support MWAIT instructions by checking the field MONITOR (bit 3) on ECX. Run this run cpuid -f and check the results. For example :

→ ./bin/cpuid -f

For each feature, a value of 1 means it is available, 0 means it is not
ECX Features:
Bit  0 (SSE3        ): 1
Bit  1 (PCLMULQDQ   ): 1
Bit  2 (DTES64      ): 1
Bit  3 (MONITOR     ): 1

We can see a 1 for MONITOR which means that this CPU supports MWAIT hints.

Usage

Usage: cpuid [options]
Options
  -h : Show this help message
  -p : Display power and thermal capacities
  -v : Display CPU vendor information
  -f : Display CPU features

Build

To build the binaries, simply run :

make

And look to bin/cpuid for the compiled binaries.

You need gcc to compile this tool

Ressources

• Main source : this amazing site about the x86/ARM64 arch
• Details about features : wikipedia