fsm-benchmarks

This repo contains benchmarks for C++ state machine libraries.

It has been originally created to test various optimizations of the Boost MSM library.

Benchmark scenarios

The benchmarks are inspired by the fsm-benchmark repository.

Header inclusion:

No instantiation of a state machine, only the headers of the library are included.

Large state machine:

Same benchmark as tested in fsm-benchmark.

Large hierarchical state machine:

This benchmarks is an extension of the large state machine and consists of a hierarchical structure of 3 state machines:

• fsm0 is the root state machine

• fsm1 is contained in fsm0

• fsm2 is contained in fsm1

The events handled by each state machine overlap with each other to simulate transition conflicts.

Tested libraries

The following libraries are benchmarked:

MSM:

MSM is used with 3 back-ends back, back11 and backmp11. The back-end backmp11 is a recent addition. For more details about the applied optimizations and changes to previous back-ends take a look at the backmp11’s README.

Only the functor frontend is used in the benchmarks. The following backend configurations are tested:

• back backend with favor_runtime_speed and favor_compile_time compile policies

• back11 backend

• backmp11 backend with favor_runtime_speed and favor_compile_time compile policies

Last run was done on commit 158beca9aa0a08f83e005e536fd9bae21637d51b.

SML:

SML is tested with a default configuration.

Last run was done on commit 0bdc4f593a3a1cc5bb45e0464c0923683d099d86.

Benchmark results

The benchmark results will be updated every once in a while in case one of the libraries has performance-relevant updates for the benchmarks.

Following results are from a benchmark run from 2025-11-22 with the following HW & SW:

• Intel i7-6700K @4GHZ, 32 GB RAM

• Clang 19.1.4, RelWithDebInfo, C++20

• CUs are compiled one-by-one except the multi_cu benchmark for MSM with backmp11 & favor_compile_time

Header inclusion

	Compile / sec	RAM / MB
back	2.3	223
back_favor_compile_time	2.3	223
back11	2.3	223
backmp11	0.9	148
backmp11_favor_compile_time	1.2	152
sml	0.1	94

Large state machine

	Compile / sec	RAM / MB	Runtime / sec
back	18	953	7
back_favor_compile_time	21	1000	8
back11	43	2794	7
backmp11	3	239	3
backmp11_favor_compile_time	3	220	13
sml	12	363	3

Large hierarchical state machine

	Compile / sec	RAM / MB	Runtime / sec
back	68	2849	23
back_favor_compile_time	80	2551	261
backmp11	11	472	10
backmp11_favor_compile_time	6	288	40
backmp11_favor_compile_time_multi_cu	5	~925	40
sml	48	1128	11