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`File.join` is a hotspot for common libraries such as Zeitwerk and Bootsnap. It has a fairly flexible signature, but 99% of the time it's called with just two (or a small number of) UTF-8 strings. If we optimistically optimize for that use case we can cut down a large number of type and encoding checks, significantly speeding up the method. The one remaining expensive check we could try to optimize is `str_null_check`. Given it's common to use the same base string for joining, we could memoize it. Also we could precompute it for literal strings. ``` compare-ruby: ruby 4.1.0dev (2026-01-17T14:40:03Z master 00a3b71eaf) +PRISM [arm64-darwin25] built-ruby: ruby 4.1.0dev (2026-01-18T12:10:38Z spedup-file-join 069bab58d4) +PRISM [arm64-darwin25] warming up.... | |compare-ruby|built-ruby| |:-------------|-----------:|---------:| |two_strings | 2.475M| 9.444M| | | -| 3.82x| |many_strings | 551.975k| 2.346M| | | -| 4.25x| |array | 514.946k| 522.034k| | | -| 1.01x| |mixed | 621.236k| 633.189k| | | -| 1.02x| ```
ruby/benchmark
This directory has benchmark definitions to be run with benchmark_driver.gem.
Normal usage
Execute gem install benchmark_driver and run a command like:
# Run a benchmark script with the ruby in the $PATH
benchmark-driver benchmark/app_fib.rb
# Run benchmark scripts with multiple Ruby executables or options
benchmark-driver benchmark/*.rb -e /path/to/ruby -e '/path/to/ruby --jit'
# Or compare Ruby versions managed by rbenv
benchmark-driver benchmark/*.rb --rbenv '2.5.1;2.6.0-preview2 --jit'
# You can collect many metrics in many ways
benchmark-driver benchmark/*.rb --runner memory --output markdown
# Some are defined with YAML for complex setup or accurate measurement
benchmark-driver benchmark/*.yml
See also:
benchmark-driver --help
Usage: benchmark-driver [options] RUBY|YAML...
-r, --runner TYPE Specify runner type: ips, time, memory, once, block (default: ips)
-o, --output TYPE Specify output type: compare, simple, markdown, record, all (default: compare)
-e, --executables EXECS Ruby executables (e1::path1 arg1; e2::path2 arg2;...)
--rbenv VERSIONS Ruby executables in rbenv (x.x.x arg1;y.y.y arg2;...)
--repeat-count NUM Try benchmark NUM times and use the fastest result or the worst memory usage
--repeat-result TYPE Yield "best", "average" or "worst" result with --repeat-count (default: best)
--alternate Alternate executables instead of running the same executable in a row with --repeat-count
--bundler Install and use gems specified in Gemfile
--filter REGEXP Filter out benchmarks with given regexp
--run-duration SECONDS Warmup estimates loop_count to run for this duration (default: 3)
--timeout SECONDS Timeout ruby command execution with timeout(1)
-v, --verbose Verbose mode. Multiple -v options increase visibility (max: 2)
make benchmark
Using make benchmark, make update-benchmark-driver automatically downloads
the supported version of benchmark_driver, and it runs benchmarks with the downloaded
benchmark_driver.
# Run all benchmarks with the ruby in the $PATH and the built ruby
make benchmark
# Or compare with specific ruby binary
make benchmark COMPARE_RUBY="/path/to/ruby --jit"
# Run vm benchmarks
make benchmark ITEM=vm
# Run some limited benchmarks in ITEM-matched files
make benchmark ITEM=vm OPTS=--filter=block
# You can specify the benchmark by an exact filename instead of using the default argument:
# ARGS = $$(find $(srcdir)/benchmark -maxdepth 1 -name '*$(ITEM)*.yml' -o -name '*$(ITEM)*.rb')
make benchmark ARGS=benchmark/erb_render.yml
# You can specify any option via $OPTS
make benchmark OPTS="--help"
# With `make benchmark`, some special runner plugins are available:
# -r peak, -r size, -r total, -r utime, -r stime, -r cutime, -r cstime
make benchmark ITEM=vm_bigarray OPTS="-r peak"