Introduce GC benchmarks

benchmarks.yml

@@ -74,6 +74,11 @@ binarytrees:
 blurhash:
   desc: blurhash (blurred preview image) calculation
   ractor: true
+gcbench:
+  desc: Ellis-Kovac-Boehm GCBench builds binary trees of various depths to exercise GC marking, sweeping, and write barriers.
+  category: gc
+  single_file: true
+  default_harness: harness-gc
 erubi:
   desc: erubi compiles a simple Erb template into a method with erubi, then times evaluating that method.
   ractor: true

benchmarks/gcbench.rb

@@ -0,0 +1,90 @@
+# Ellis-Kovac-Boehm GCBench
+#
+# Adapted from the benchmark by John Ellis and Pete Kovac (Post Communications),
+# modified by Hans Boehm (Silicon Graphics), translated to Ruby by Noel Padavan
+# and Chris Seaton. Adapted for yjit-bench by Matt Valentine-House.
+#
+# Builds balanced binary trees of various depths to generate objects with a range
+# of lifetimes. Two long-lived structures (a tree and a float array) are kept
+# alive throughout to model applications that maintain persistent heap data.
+#
+# Tree construction uses both top-down (populate — creates old-to-young pointers,
+# exercises write barriers) and bottom-up (make_tree — young-to-young only).
+
+require_relative '../harness/loader'
+
+class GCBench
+  class Node
+    attr_accessor :left, :right, :i, :j
+
+    def initialize(left = nil, right = nil)
+      @left = left
+      @right = right
+      @i = 0
+      @j = 0
+    end
+  end
+
+  STRETCH_TREE_DEPTH   = 18
+  LONG_LIVED_TREE_DEPTH = 16
+  ARRAY_SIZE            = 500_000
+  MIN_TREE_DEPTH        = 4
+  MAX_TREE_DEPTH        = 16
+
+  def self.tree_size(depth)
+    (1 << (depth + 1)) - 1
+  end
+
+  def self.num_iters(depth)
+    2 * tree_size(STRETCH_TREE_DEPTH) / tree_size(depth)
+  end
+
+  # Top-down: assigns children to an existing (older) node — old-to-young pointers.
+  def self.populate(depth, node)
+    if depth > 0
+      depth -= 1
+      node.left = Node.new
+      node.right = Node.new
+      populate(depth, node.left)
+      populate(depth, node.right)
+    end
+  end
+
+  # Bottom-up: children allocated before parent — young-to-young pointers only.
+  def self.make_tree(depth)
+    if depth <= 0
+      Node.new
+    else
+      Node.new(make_tree(depth - 1), make_tree(depth - 1))
+    end
+  end
+
+  def self.time_construction(depth)
+    n = num_iters(depth)
+
+    n.times do
+      node = Node.new
+      populate(depth, node)
+    end
+
+    n.times do
+      make_tree(depth)
+    end
+  end
+end
+
+# Stretch the heap before measurement
+GCBench.make_tree(GCBench::STRETCH_TREE_DEPTH)
+
+# Long-lived objects that persist across all iterations
+long_lived_tree = GCBench::Node.new
+GCBench.populate(GCBench::LONG_LIVED_TREE_DEPTH, long_lived_tree)
+
+long_lived_array = Array.new(GCBench::ARRAY_SIZE)
+(GCBench::ARRAY_SIZE / 2).times { |i| long_lived_array[i + 1] = 1.0 / (i + 1) }
+
+run_benchmark(10) do
+  GCBench::MIN_TREE_DEPTH.step(GCBench::MAX_TREE_DEPTH, 2) do |depth|
+    GCBench.time_construction(depth)
+  end
+end

harness-gc/harness.rb

@@ -0,0 +1,112 @@
+require_relative "../harness/harness-common"
+
+WARMUP_ITRS = Integer(ENV.fetch('WARMUP_ITRS', 15))
+MIN_BENCH_ITRS = Integer(ENV.fetch('MIN_BENCH_ITRS', 10))
+MIN_BENCH_TIME = Integer(ENV.fetch('MIN_BENCH_TIME', 10))
+
+puts RUBY_DESCRIPTION
+
+def realtime
+  r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+  yield
+  Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
+end
+
+def gc_stat_heap_snapshot
+  return {} unless GC.respond_to?(:stat_heap)
+  GC.stat_heap
+end
+
+def gc_stat_heap_delta(before, after)
+  delta = {}
+  after.each do |heap_idx, after_stats|
+    before_stats = before[heap_idx] || {}
+    heap_delta = {}
+    after_stats.each do |key, val|
+      next unless val.is_a?(Numeric) && before_stats.key?(key)
+      heap_delta[key] = val - before_stats[key]
+    end
+    delta[heap_idx] = heap_delta unless heap_delta.empty?
+  end
+  delta
+end
+
+def run_benchmark(_num_itrs_hint, **, &block)
+  times = []
+  marking_times = []
+  sweeping_times = []
+  gc_counts = []
+  gc_heap_deltas = []
+  total_time = 0
+  num_itrs = 0
+
+  has_marking = GC.stat.key?(:marking_time)
+  has_sweeping = GC.stat.key?(:sweeping_time)
+
+  header = "itr:   time"
+  header << "   marking" if has_marking
+  header << "  sweeping" if has_sweeping
+  header << "  gc_count"
+  puts header
+
+  begin
+    gc_before = GC.stat
+    heap_before = gc_stat_heap_snapshot
+
+    time = realtime(&block)
+    num_itrs += 1
+
+    gc_after = GC.stat
+    heap_after = gc_stat_heap_snapshot
+
+    time_ms = (1000 * time).to_i
+    mark_delta = has_marking ? gc_after[:marking_time] - gc_before[:marking_time] : 0
+    sweep_delta = has_sweeping ? gc_after[:sweeping_time] - gc_before[:sweeping_time] : 0
+    count_delta = gc_after[:count] - gc_before[:count]
+
+    itr_str = "%4s %6s" % ["##{num_itrs}:", "#{time_ms}ms"]
+    itr_str << " %9.1fms" % mark_delta if has_marking
+    itr_str << " %9.1fms" % sweep_delta if has_sweeping
+    itr_str << " %9d" % count_delta
+    puts itr_str
+
+    times << time
+    marking_times << mark_delta
+    sweeping_times << sweep_delta
+    gc_counts << count_delta
+    gc_heap_deltas << gc_stat_heap_delta(heap_before, heap_after)
+    total_time += time
+  end until num_itrs >= WARMUP_ITRS + MIN_BENCH_ITRS and total_time >= MIN_BENCH_TIME
+
+  warmup_range = 0...WARMUP_ITRS
+  bench_range = WARMUP_ITRS..-1
+
+  extra = {}
+  extra["gc_marking_time_warmup"] = marking_times[warmup_range]
+  extra["gc_marking_time_bench"] = marking_times[bench_range]
+  extra["gc_sweeping_time_warmup"] = sweeping_times[warmup_range]
+  extra["gc_sweeping_time_bench"] = sweeping_times[bench_range]
+  extra["gc_count_warmup"] = gc_counts[warmup_range]
+  extra["gc_count_bench"] = gc_counts[bench_range]
+  extra["gc_stat_heap_deltas"] = gc_heap_deltas[bench_range]
+
+  return_results(times[warmup_range], times[bench_range], **extra)
+
+  non_warmups = times[bench_range]
+  if non_warmups.size > 1
+    non_warmups_ms = ((non_warmups.sum / non_warmups.size) * 1000.0).to_i
+    puts "Average of last #{non_warmups.size}, non-warmup iters: #{non_warmups_ms}ms"
+
+    if has_marking
+      mark_bench = marking_times[bench_range]
+      avg_mark = mark_bench.sum / mark_bench.size
+      puts "Average marking time: %.1fms" % avg_mark
+    end
+
+    if has_sweeping
+      sweep_bench = sweeping_times[bench_range]
+      avg_sweep = sweep_bench.sum / sweep_bench.size
+      puts "Average sweeping time: %.1fms" % avg_sweep
+    end
+  end
+end

harness/harness-common.rb

@@ -75,8 +75,13 @@ def get_rss
     # Collect our own peak mem usage as soon as reasonable after finishing the last iteration.
     # This method is only accurate to kilobytes, but is nicely portable and doesn't require
     # any extra gems/dependencies.
-    mem = `ps -o rss= -p #{Process.pid}`
-    1024 * Integer(mem)
+    begin
+      mem = `ps -o rss= -p #{Process.pid}`
+      1024 * Integer(mem)
+    rescue ArgumentError, Errno::ENOENT
+      # ps failed (e.g. Nix procps on macOS). Fall back to peak RSS via getrusage.
+      get_maxrss || 0
+    end
   end
 end
 
@@ -135,11 +140,12 @@ def get_maxrss
 yb_env_var = ENV.fetch("RESULT_JSON_PATH", default_path)
 YB_OUTPUT_FILE = File.expand_path yb_env_var
 
-def return_results(warmup_iterations, bench_iterations)
+def return_results(warmup_iterations, bench_iterations, **extra)
   ruby_bench_results = {
     "RUBY_DESCRIPTION" => RUBY_DESCRIPTION,
     "warmup" => warmup_iterations,
     "bench" => bench_iterations,
+    **extra,
   }
 
   # Collect JIT stats before loading any additional code.

lib/benchmark_runner.rb

@@ -48,7 +48,7 @@ def write_csv(output_path, ruby_descriptions, table)
     end
 
     # Build output text string with metadata, table, and legend
-    def build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: false)
+    def build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: false, include_gc: false)
       base_name, *other_names = ruby_descriptions.keys
 
       output_str = +""
@@ -68,6 +68,10 @@ def build_output_text(ruby_descriptions, table, format, bench_failures, include_
           if include_rss
             output_str << "- RSS #{base_name}/#{name}: ratio of #{base_name}/#{name} RSS. Higher is better for #{name}. Above 1 means lower memory usage.\n"
           end
+          if include_gc
+            output_str << "- mark #{base_name}/#{name}: ratio of GC marking time. Higher is better for #{name}. Above 1 represents faster marking.\n"
+            output_str << "- sweep #{base_name}/#{name}: ratio of GC sweeping time. Higher is better for #{name}. Above 1 represents faster sweeping.\n"
+          end
         end
         output_str << "- ***: p < 0.001, **: p < 0.01, *: p < 0.05 (Welch's t-test)\n"
       end

lib/benchmark_runner/cli.rb

@@ -109,7 +109,7 @@ def run
       BenchmarkRunner.write_csv(output_path, ruby_descriptions, table)
 
       # Save the output in a text file that we can easily refer to
-      output_str = BenchmarkRunner.build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: args.rss)
+      output_str = BenchmarkRunner.build_output_text(ruby_descriptions, table, format, bench_failures, include_rss: args.rss, include_gc: builder.include_gc?)
       out_txt_path = output_path + ".txt"
       File.open(out_txt_path, "w") { |f| f.write output_str }