Benchmark results on the benchmark from https://chrisseaton.com/truffleruby/ruby-stm/

_table.md

Ruby Implementation	Speedup relative to 2.7.2
Ruby 2.7.2	1.00x
Ruby 2.7.2 --jit	1.16x
Ruby 3 dev	0.81x
Ruby 3 dev --jit	1.08x
TruffleRuby CE 20.2 --jvm	19.73x
TruffleRuby EE 20.2 --jvm	31.54x

The median i/s result out of 3 is used to compute speedups.

These results were run with this commit + changes.diff below to get a better idea of variance.

changes.diff

diff --git a/bench/sequential.rb b/bench/sequential.rb
index e0d7bf8..bdd2a8d 100644
--- a/bench/sequential.rb
+++ b/bench/sequential.rb
@@ -1,5 +1,7 @@
 # This benchmark solves the testBoard.
 
+puts RUBY_DESCRIPTION
+
 require 'benchmark/ips'
 
 require_relative '../lib/lee'
@@ -86,8 +88,9 @@ def solve_board(board)
 end
 
 Benchmark.ips do |x|
-  x.time = 30
-  x.warmup = 30
+  x.time = 10
+  x.warmup = 10
+  x.iterations = 3
 
   x.report('testBoard') do
     solve_board(board)
diff --git a/lib/lee/board.rb b/lib/lee/board.rb
index 111076c..f933090 100644
--- a/lib/lee/board.rb
+++ b/lib/lee/board.rb
@@ -1,3 +1,5 @@
+require 'set'
+
 module Lee
 
   # A point is a location on the board.

times.txt

$ ruby bench/sequential.rb
ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-linux]
Warming up --------------------------------------
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
Calculating -------------------------------------
           testBoard      1.214  (± 0.0%) i/s -     13.000  in  10.714388s
           testBoard      1.214  (± 0.0%) i/s -     13.000  in  10.711989s
           testBoard      1.215  (± 0.0%) i/s -     13.000  in  10.702990s

$ ruby --jit bench/sequential.rb
ruby 2.7.2p137 (2020-10-01 revision 5445e04352) +JIT [x86_64-linux]
Warming up --------------------------------------
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
Calculating -------------------------------------
           testBoard      1.411  (± 0.0%) i/s -     15.000  in  10.631961s
           testBoard      1.410  (± 0.0%) i/s -     15.000  in  10.643642s
           testBoard      1.411  (± 0.0%) i/s -     15.000  in  10.636146s

$ ruby bench/sequential.rb
ruby 3.0.0dev (2020-10-30T12:45:23Z master 66bf743b93) [x86_64-linux]
Warming up --------------------------------------
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
Calculating -------------------------------------
           testBoard      0.984  (± 0.0%) i/s -     10.000  in  10.158082s
           testBoard      0.989  (± 0.0%) i/s -     10.000  in  10.112835s
           testBoard      0.988  (± 0.0%) i/s -     10.000  in  10.119596s

$ ruby --jit bench/sequential.rb
ruby 3.0.0dev (2020-10-30T12:45:23Z master 66bf743b93) +JIT [x86_64-linux]
Warming up --------------------------------------
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
           testBoard     1.000  i/100ms
Calculating -------------------------------------
           testBoard      1.304  (± 0.0%) i/s -     14.000  in  10.734479s
           testBoard      1.321  (± 0.0%) i/s -     14.000  in  10.597937s
           testBoard      1.315  (± 0.0%) i/s -     14.000  in  10.646729s

$ ruby --jvm bench/sequential.rb
truffleruby 20.2.0, like ruby 2.6.6, GraalVM CE JVM [x86_64-linux]
Warming up --------------------------------------
           testBoard     1.000  i/100ms
           testBoard     2.000  i/100ms
           testBoard     2.000  i/100ms
Calculating -------------------------------------
           testBoard     23.898  (± 4.2%) i/s -    240.000  in  10.051196s
           testBoard     23.948  (± 4.2%) i/s -    240.000  in  10.027479s
           testBoard     23.952  (± 0.0%) i/s -    240.000  in  10.021410s

$ ruby --jvm bench/sequential.rb
truffleruby 20.2.0, like ruby 2.6.6, GraalVM EE JVM [x86_64-linux]
Warming up --------------------------------------
           testBoard     1.000  i/100ms
           testBoard     3.000  i/100ms
           testBoard     3.000  i/100ms
Calculating -------------------------------------
           testBoard     38.106  (± 2.6%) i/s -    381.000  in  10.010918s
           testBoard     38.285  (± 2.6%) i/s -    384.000  in  10.035698s
           testBoard     38.436  (± 2.6%) i/s -    387.000  in  10.070958s