Merge pull request #3989 from DataDog/ivoanjo/prof-10589-gvl-profiling-microbenchmark

[PROF-10589] Add microbenchmark for GVL profiling sampling

Author: ivoanjo

benchmarks/profiler_sample_gvl.rb

@@ -0,0 +1,86 @@
+# Used to quickly run benchmark under RSpec as part of the usual test suite, to validate it didn't bitrot
+VALIDATE_BENCHMARK_MODE = ENV['VALIDATE_BENCHMARK'] == 'true'
+
+return unless __FILE__ == $PROGRAM_NAME || VALIDATE_BENCHMARK_MODE
+
+require_relative 'benchmarks_helper'
+
+if RUBY_VERSION < '3.2'
+  if VALIDATE_BENCHMARK_MODE
+    # To simplify things, we allow this benchmark to be run in VALIDATE_BENCHMARK_MODE even though it's a no-op
+    $stderr.puts "Skipping benchmark because it requires Ruby 3.2 or newer"
+    return
+  else
+    raise 'This benchmark requires Ruby 3.2 or newer'
+  end
+end
+
+# This benchmark measures the performance of the main stack sampling loop of the profiler
+
+class ProfilerSampleGvlBenchmark
+  # This is needed because we're directly invoking the collector through a testing interface; in normal
+  # use a profiler thread is automatically used.
+  PROFILER_OVERHEAD_STACK_THREAD = Thread.new { sleep }
+
+  def initialize
+    create_profiler
+    @target_thread = thread_with_very_deep_stack
+
+    # Sample once to trigger thread context creation for all threads (including @target_thread)
+    Datadog::Profiling::Collectors::ThreadContext::Testing._native_sample(@collector, PROFILER_OVERHEAD_STACK_THREAD)
+  end
+
+  def create_profiler
+    @recorder = Datadog::Profiling::StackRecorder.new(
+      cpu_time_enabled: true,
+      alloc_samples_enabled: false,
+      heap_samples_enabled: false,
+      heap_size_enabled: false,
+      heap_sample_every: 1,
+      timeline_enabled: true,
+    )
+    @collector = Datadog::Profiling::Collectors::ThreadContext.for_testing(
+      recorder: @recorder,
+      waiting_for_gvl_threshold_ns: 0,
+      timeline_enabled: true,
+    )
+  end
+
+  def thread_with_very_deep_stack(depth: 200)
+    deep_stack = proc do |n|
+      if n > 0
+        deep_stack.call(n - 1)
+      else
+        sleep
+      end
+    end
+
+    Thread.new { deep_stack.call(depth) }.tap { |t| t.name = "Deep stack #{depth}" }
+  end
+
+  def run_benchmark
+    Benchmark.ips do |x|
+      benchmark_time = VALIDATE_BENCHMARK_MODE ? { time: 0.01, warmup: 0 } : { time: 20, warmup: 2 }
+      x.config(
+        **benchmark_time,
+      )
+
+      x.report("gvl benchmark samples") do
+        Datadog::Profiling::Collectors::ThreadContext::Testing._native_on_gvl_waiting(@target_thread)
+        Datadog::Profiling::Collectors::ThreadContext::Testing._native_on_gvl_running(@target_thread)
+        Datadog::Profiling::Collectors::ThreadContext::Testing._native_sample_after_gvl_running(@collector, @target_thread)
+      end
+
+      x.save! "#{File.basename(__FILE__)}-results.json" unless VALIDATE_BENCHMARK_MODE
+      x.compare!
+    end
+
+    @recorder.serialize!
+  end
+end
+
+puts "Current pid is #{Process.pid}"
+
+ProfilerSampleGvlBenchmark.new.instance_exec do
+  run_benchmark
+end

benchmarks/run_all.sh

@@ -14,6 +14,7 @@ for file in \
   `dirname "$0"`/profiler_memory_sample_serialize.rb \
   `dirname "$0"`/profiler_sample_loop_v2.rb \
   `dirname "$0"`/profiler_sample_serialize.rb \
+  `dirname "$0"`/profiler_sample_gvl.rb \
   `dirname "$0"`/tracing_trace.rb;
 do
   bundle exec ruby "$file"

spec/datadog/profiling/validate_benchmarks_spec.rb

@@ -17,6 +17,7 @@
     "profiler_memory_sample_serialize",
     "profiler_sample_loop_v2",
     "profiler_sample_serialize",
+    "profiler_sample_gvl",
   ].freeze
 
   benchmarks_to_validate.each do |benchmark|