Tokios performance is measured using criterion for comprehensive statistics-driven benchmarking.
Benchmarks are defined in the benches subdirectory and can be run using the cargo bench subcommand (eg cargo bench). To run a specific benchmark, you can use cargo bench --bench <name>, where <name> is one of the benchmarks defined in the Cargo.toml file under a [[bench]] section.
Flamegraph is a powerful rust crate for generating profile visualizations, that is graphing the time a program spends in each function. Functions called during execution are displayed as horizontal rectangles with the width proportional to the time spent in that function. As the call stack grows (think nested function invocations), the rectangles are stacked vertically. This provides a powerful visualization for quickly understanding which parts of a codebase take up disproportionate amounts of time.
Check out Brendan Gregg's Flame Graphs blog post if you're interested in learning more about flamegraphs and performance visualizations in general.
To generate a flamegraph for tokios, you can use the cargo flamegraph subcommand. For example, to generate a flamegraph for the client example, you can run:
cargo flamegraph --example client -o ./flamegraphs/client.svg