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Show Major/minor stats on per-iteration gc benchmarks #489

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09a1d20
Show Major/minor stats on per-iteration gc benchmarks
eightbitraptor Mar 12, 2026
7b961bb
Add some details about need_major_by
eightbitraptor Mar 12, 2026
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49 changes: 49 additions & 0 deletions harness-gc/harness.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -36,17 +36,24 @@ def run_benchmark(_num_itrs_hint, **, &block)
marking_times = []
sweeping_times = []
gc_counts = []
major_counts = []
minor_counts = []
gc_heap_deltas = []
major_reasons_per_itr = []
total_time = 0
num_itrs = 0

has_marking = GC.stat.key?(:marking_time)
has_sweeping = GC.stat.key?(:sweeping_time)
has_major_by = GC.respond_to?(:latest_gc_info) && GC.latest_gc_info.key?(:major_by)

header = "itr: time"
header << " marking" if has_marking
header << " sweeping" if has_sweeping
header << " gc_count"
header << " major"
header << " minor"
header << " maj/min"
puts header

begin
Expand All @@ -63,18 +70,35 @@ def run_benchmark(_num_itrs_hint, **, &block)
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]
major_delta = gc_after[:major_gc_count] - gc_before[:major_gc_count]
minor_delta = gc_after[:minor_gc_count] - gc_before[:minor_gc_count]
ratio_str = minor_delta > 0 ? "%.2f" % (major_delta.to_f / minor_delta) : "-"

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
itr_str << " %9d" % major_delta
itr_str << " %9d" % minor_delta
itr_str << " %9s" % ratio_str
puts itr_str

times << time
marking_times << mark_delta
sweeping_times << sweep_delta
gc_counts << count_delta
major_counts << major_delta
minor_counts << minor_delta
gc_heap_deltas << gc_stat_heap_delta(heap_before, heap_after)
if has_major_by && major_delta > 0
# latest_gc_info only reflects the most recent GC event — if a minor
# GC ran after the last major, the reason is lost (shows :none).
reason = GC.latest_gc_info[:major_by]
reason = :unknown if reason.nil? || reason == :none
major_reasons_per_itr << { reason => major_delta }
else
major_reasons_per_itr << {}
end
total_time += time
end until num_itrs >= WARMUP_ITRS + MIN_BENCH_ITRS and total_time >= MIN_BENCH_TIME

Expand All @@ -88,8 +112,22 @@ def run_benchmark(_num_itrs_hint, **, &block)
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_major_count_warmup"] = major_counts[warmup_range]
extra["gc_major_count_bench"] = major_counts[bench_range]
extra["gc_minor_count_warmup"] = minor_counts[warmup_range]
extra["gc_minor_count_bench"] = minor_counts[bench_range]
extra["gc_stat_heap_deltas"] = gc_heap_deltas[bench_range]

if has_major_by
aggregate_reasons = ->(range) {
tally = Hash.new(0)
major_reasons_per_itr[range].each { |h| h.each { |r, c| tally[r] += c } }
tally.transform_keys(&:to_s)
}
extra["gc_major_reasons_warmup"] = aggregate_reasons[warmup_range]
extra["gc_major_reasons_bench"] = aggregate_reasons[bench_range]
end

return_results(times[warmup_range], times[bench_range], **extra)

non_warmups = times[bench_range]
Expand All @@ -108,5 +146,16 @@ def run_benchmark(_num_itrs_hint, **, &block)
avg_sweep = sweep_bench.sum / sweep_bench.size
puts "Average sweeping time: %.1fms" % avg_sweep
end

if has_major_by
bench_reasons = extra["gc_major_reasons_bench"]
if bench_reasons.any?
total = bench_reasons.values.sum
puts "\nMajor GC triggers (#{total} across bench iterations):"
bench_reasons.sort_by { |_, count| -count }.each do |reason, count|
puts " %-20s %d" % [reason, count]
end
end
end
end
end
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