x86-64-level - Get the x86-64 Microarchitecture Level on the Current Machine

TL;DR: The x86-64-level tool identifies if the current CPU supports x86-64-v1, x86-64-v2, x86-64-v3, or x86-64-v4, e.g.

$ x86-64-level
3

Background

x86-64 is a 64-bit version of the x86 CPU instruction set supported by AMD and Intel CPUs, among others. Since the first generations of CPUs, more low-level CPU features have been added over the years. The x86-64 CPU features can be grouped into four CPU microarchitecture levels:

Level	CPU Features
x86-64-v1	CMOV, CX8, FPU, FXSR, MMX, OSFXSR, SCE, SSE, SSE2
x86-64-v2	CMPXCHG16B, LAHF-SAHF, POPCNT, SSE3, SSE4_1, SSE4_2, SSSE3
x86-64-v3	AVX, AVX2, BMI1, BMI2, F16C, FMA, LZCNT, MOVBE, OSXSAVE
x86-64-v4	AVX512F, AVX512BW, AVX512CD, AVX512DQ, AVX512VL

The x86-64-v1 level is the same as the original, baseline x86-64 level. These levels are subsets of each other, i.e. x86-64-v1 ⊂ x86-64-v2 ⊂ x86-64-v3 ⊂ x86-64-v4. For a CPU to support a level, it must support all CPU features of that version level, and, because they are subsets of each other, all those of the lower versions.

Software can be written so that they use the most powerful set of CPU features available. This optimization happens at compile time and allows the software to run more efficiently. However, a software binary that was compiled towards the x86-64-v4 level cannot run on an older machine with a CPU that only supports, say, x86-64-v3. If we attempt to run the software on the older machine, it will crash and we might get something like:

 *** caught illegal operation ***
address 0x2b3a8b234ccd, cause 'illegal operand'

or

Illegal instruction (core dumped)

This is because the older CPU does not understand one of the CPU instructions ("operands"). Note that the software might not crash each time. It will only do so if it reaches the part of the code that uses a CPU instruction that is not recognized by the current CPU.

In contrast, if we compile the software towards the older x86-64-v3 machine, the produced binary will only use x86-64-v3 instructions and will therefor also run on the newer x86-64-v4 machine.

Tips: If you work on a high-performance compute (HPC) environment with compute nodes of different generations of CPUs, and you want a smooth ride, compile your software tools to use the oldest x86-64 level. This won't make best use of the more modern CPUs, but the software will run on all compute nodes and you won't run into the 'caught illegal operation' problem.

Usage

Finding CPU's x86-64 level

This tool, x86-64-level, allows you to query which x86-64 level the CPU on current machine supports. For example,

$ x86-64-level
3

and

$ level=$(x86-64-level)
$ echo "x86-64-v${level}"
x86-64-v3

If you want to get an explanation for the identified level, specify option --verbose, e.g.

$ x86-64-level --verbose
Identified x86-64-v3, because x86-64-v4 requires 'avx512f', which
is not supported by this CPU [Intel(R) Core(TM) i7-8650U CPU @ 1.90GHz]
3

Assert minimum x86-64 level

To test if the CPU supports a minimum level of x86-64, use the --assert=<level> option. For example,

$ x86-64-level
3

$ x86-64-level --assert=2
$ echo $?
0

$ x86-64-level --assert=3
$ echo $?
0

$ x86-64-level --assert=4
The CPU [Intel(R) Core(TM) i7-8650U CPU @ 1.90GHz] on this host ('dev2')
supports x86-64-v3, which is less than the required x86-64-v4
$ echo $?
1

To use this as a gatekeeper in a shell script, add:

x86-64-level --assert=4 || exit 1

This will output that error message (to the standard error) and exit the script with exit code 1, if, and only if, the current machine does not support x86-64-v4. In all other cases, it continues silently.

Installation

The x86-64-level tool is a standalone Linux Bash script that queries /proc/cpuinfo. To install it, download the script and set the executable flag;

$ curl -L -O https://raw.githubusercontent.com/HenrikBengtsson/x86-64-level/main/x86-64-level
$ chmod ugo+x x86-64-level

To verify it works, try:

$ ./x86-64-level --help
$ ./x86-64-level --version
$ ./x86-64-level

Alternative, you may be able to install x86-64-level as a package for your Linux distribution:

License

The content of this repository is released under the CC BY-SA 4.0 license.

Authors

• Henrik Bengtsson (expanded on Gilles' implementation)
• StackExchange user Gilles
• StackExchange user gioele