Add benchmark for gem loading

benchmarks/tracing_trace.rb

@@ -4,6 +4,8 @@
 return unless __FILE__ == $PROGRAM_NAME || VALIDATE_BENCHMARK_MODE
 
 require 'benchmark/ips'
+require 'open3'
+
 require 'ddtrace'
 
 class TracingTraceBenchmark
@@ -163,6 +165,36 @@ def benchmark_propagation_trace_context
       end
     end
   end
+
+  def benchmark_gem_loading
+    # This benchmark needs to be run in a clean environment where ddtrace is not loaded yet
+    output, status = Open3.capture2e('ruby', stdin_data: <<-RUBY)
+      raise "Datadog is already loaded" if defined?(::Datadog)
+
+      VALIDATE_BENCHMARK_MODE = ENV['VALIDATE_BENCHMARK'] == 'true'
+      require 'benchmark/ips'
+      
+      Benchmark.ips do |x|
+        # Gem loading is quite slower than the other microbenchmarks
+        benchmark_time = VALIDATE_BENCHMARK_MODE ? { time: 0.001, warmup: 0 } : { time: 60, warmup: 5 }
+        x.config(**benchmark_time)
+  
+        x.report("Gem loading") do
+          pid = fork { require 'ddtrace' }
+  
+          _, status = Process.wait2(pid)
+          raise unless status.success?
+        end
+  
+        x.save! "#{__FILE__}-results.json" unless VALIDATE_BENCHMARK_MODE
+        x.compare!
+      end
+    RUBY
+
+    print output
+
+    raise "Benchmark failed with status #{status}: #{output}" unless status.success?
+  end
 end
 
 puts "Current pid is #{Process.pid}"
@@ -183,4 +215,5 @@ def run_benchmark(&block)
   run_benchmark { benchmark_to_digest_continue }
   run_benchmark { benchmark_propagation_datadog }
   run_benchmark { benchmark_propagation_trace_context }
+  run_benchmark { benchmark_gem_loading }
 end