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Small set of benchmarks and scripts for the YJIT Ruby JIT compiler project, which lives in the Shopify/yjit repository.

The benchmarks are found in the benchmarks directory. Individual Ruby files in benchmarks are microbenchmarks. Subdirectories under benchmarks are larger macrobenchmarks. Each benchmark relies on a harness found in ./harness/harness.rb. The harness controls the number of times a benchmark is run, and writes timing values into an output file.

The run_benchmarks.rb script (optional) traverses the benchmarks directory and runs the benchmarks in there. It reads the output file written by the benchmarking harness. The output is written to multiple files at the end -- CSV, text and JSON -- so that results can be easily viewed or graphed in any spreadsheet editor.


Clone this repository:

git clone yjit-bench

Benchmarking YJIT

yjit-bench supports benchmarking any Ruby implementation. But if you want to benchmark YJIT, follow these instructions to build and install YJIT.

If you install it with the name ruby-yjit on chruby, you should enable it before running ./run_benchmarks.rb:

chruby ruby-yjit


To run all the benchmarks and record the data:

cd yjit-bench

This runs for a few minutes and produces a table like this in the console (results below not up to date):

-------------  -----------  ----------  ---------  ----------  -----------  ------------
bench          interp (ms)  stddev (%)  yjit (ms)  stddev (%)  interp/yjit  yjit 1st itr
30k_ifelse     2372.0       0.0         447.6      0.1         5.30         4.16
30k_methods    6328.3       0.0         963.4      0.0         6.57         6.25
activerecord   171.7        0.8         144.2      0.7         1.19         1.15
binarytrees    445.8        2.1         389.5      2.5         1.14         1.14
cfunc_itself   105.7        0.2         58.7       0.7         1.80         1.80
fannkuchredux  6697.3       0.1         6714.4     0.1         1.00         1.00
fib            245.3        0.1         77.1       0.4         3.18         3.19
getivar        97.3         0.9         44.3       0.6         2.19         0.98
lee            1269.7       0.9         1172.9     1.0         1.08         1.08
liquid-render  204.5        1.0         172.4      1.3         1.19         1.18
nbody          121.9        0.1         121.6      0.3         1.00         1.00
optcarrot      6260.2       0.5         4723.1     0.3         1.33         1.33
railsbench     3827.9       0.9         3581.3     1.3         1.07         1.05
respond_to     259.0        0.6         197.1      0.4         1.31         1.31
setivar        73.1         0.2         53.3       0.7         1.37         1.00
-------------  -----------  ----------  ---------  ----------  -----------  ------------

The interp/yjit column is the ratio of the average time taken by the interpreter over the average time taken by YJIT after a number of warmup iterations. Results above 1 represent speedups. For instance, 1.14 means "YJIT is 1.14 times as fast as the interpreter".

Specific categories

By default, run_benchmarks.rb runs all three benchmark categories, --category headline,other,micro. You can run only benchmarks with specific categories:

./run_benchmarks.rb --category micro

You can also only the headline benchmarks with the --headline option:

./run_benchmarks.rb --headline

Specific benchmarks

To run one or more specific benchmarks and record the data:

./run_benchmarks.rb fib lee optcarrot

Running a single benchmark

This is the easiest way to run a single benchmark. It requires no setup at all and assumes nothing about the Ruby you are benchmarking. It's also convenient for profiling, debugging, etc, especially since all benchmarked code runs in that process.

ruby benchmarks/some_benchmark.rb

Ruby options

By default, yjit-bench benchmarks the Ruby used for run_benchmarks.rb. If the Ruby has --yjit option, it compares two Ruby commands, -e "interp::ruby" and -e "yjit::ruby --yjit. However, if you specify -e yourself, you can override what Ruby is benchmarked.

# "xxx::" prefix can be used to specify a shorter name/alias, but it's optional.
./run_benchmarks.rb -e "ruby" -e "yjit::ruby --yjit"

# You could also measure only a single Ruby
./run_benchmarks.rb -e "3.1.0::/opt/rubies/3.1.0/bin/ruby"

# With --chruby, you can easily specify rubies managed by chruby
./run_benchmarks.rb --chruby "3.1.0" --chruby "3.1.0+YJIT::3.1.0 --yjit"

# ";" can be used to specify multiple executables in a single option
./run_benchmarks.rb --chruby "3.1.0;3.1.0+YJIT::3.1.0 --yjit"

YJIT options

You can use --yjit_opts to specify YJIT command-line options:

./run_benchmarks.rb --yjit_opts="--yjit-version-limit=10" fib lee optcarrot

Running pre-init code

It is possible to use run_benchmarks.rb to run arbitrary code before each benchmark run using the --with-pre-init option.

For example: to run benchmarks with GC.auto_compact enabled a pre-init.rb file can be created, containing GC.auto_compact=true, and this can be passed into the benchmarks in the following way:

./run_benchmarks.rb --with-pre-init=./pre-init.rb

This file will then be passed to the underlying Ruby interpreter with -r.


You can find several test harnesses in this repository:

  • harness - the normal default harness, with duration controlled by warmup iterations and time/count limits
  • harness-perf - a simplified harness that runs for exactly the hinted number of iterations
  • harness-bips - a harness that measures iterations/second until stable
  • harness-continuous - a harness that adjusts the batch sizes of iterations to run in stable iteration size batches
  • harness-stats - count method calls and loop iterations
  • harness-warmup - a harness which runs as long as needed to find warmed up (peak) performance

To use it, run a benchmark script directly, specifying a harness directory with -I:

ruby -Iharness benchmarks/railsbench/benchmark.rb

There is also a robust but complex CI harness in the yjit-metrics repo.

Iterations and duration

With the default harness, the number of iterations and duration can be controlled by the following environment variables:

  • WARMUP_ITRS: The number of warm-up iterations, ignored in the final comparison (default: 15)
  • MIN_BENCH_ITRS: The minimum number of benchmark iterations (default: 10)
  • MIN_BENCH_TIME: The minimum seconds for benchmark (default: 10)

You can also use --warmup, --bench, or --once to set these environment variables:

# same as: WARMUP_ITRS=2 MIN_BENCH_ITRS=3 MIN_BENCH_TIME=0 ./run_benchmarks.rb railsbench
./run_benchmarks.rb railsbench --warmup=2 --bench=3

# same as: WARMUP_ITRS=0 MIN_BENCH_ITRS=1 MIN_BENCH_TIME=0 ./run_benchmarks.rb railsbench
./run_benchmarks.rb railsbench --once

There is also a handy script for running benchmarks just once using WARMUP_ITRS=0 MIN_BENCH_ITRS=1 MIN_BENCH_TIME=0, for example with the --yjit-stats command-line option:

./ --yjit-stats benchmarks/railsbench/benchmark.rb

Using perf

There is also a harness to use Linux perf. By default, it only runs a fixed number of iterations. If PERF environment variable is present, it starts the perf subcommand after warmup.

# Use `perf record` for both warmup and benchmark
perf record ruby --yjit-perf=map -Iharness-perf benchmarks/railsbench/benchmark.rb

# Use `perf record` only for benchmark
PERF=record ruby --yjit-perf=map -Iharness-perf benchmarks/railsbench/benchmark.rb

This is the only harness that uses run_benchmark's argument, num_itrs_hint.

Measuring memory usage

--rss option of run_benchmarks.rb allows you to measure RSS after benchmark iterations.

./run_benchmarks.rb --rss

Rendering a graph

--graph option of run_benchmarks.rb allows you to render benchmark results as a graph.

# Write a graph at data/output_XXX.png (it will print the path)
./run_benchmarks.rb --graph


Before using this option, you might need to install the dependencies of Gruff:

# macOS
brew install imagemagick

# Ubuntu
sudo apt-get install libmagickwand-dev

Changing font size

You can regenerate a graph with misc/graph.rb, changing its font size.

Usage: misc/graph.rb [options] CSV_PATH
        --title SIZE                 title font size
        --legend SIZE                legend font size
        --marker SIZE                marker font size

Disabling CPU Frequency Scaling

To disable CPU frequency scaling with an Intel CPU, edit /etc/default/grub or /etc/default/grub.d/50-cloudimg-settings.cfg and add intel_pstate=no_hwp to GRUB_CMDLINE_LINUX_DEFAULT. It’s a space-separated list.


sudo update-grub
sudo reboot
sudo sh -c 'echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo'

To verify things worked:

  • cat /proc/cmdline to see the intel_pstate=no_hwp parameter is in there
  • ls /sys/devices/system/cpu/intel_pstate/ and hwp_dynamic_boost should not exist
  • cat /sys/devices/system/cpu/intel_pstate/no_turbo should say 1

Helpful docs:


Set of benchmarks for the YJIT CRuby JIT compiler and other Ruby implementations.




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