Reduce dependency requirements to enable running some benchmarks with miniruby (#308)

* Embed realtime method to remove dependency on benchmark

* Warn and skip max rss if fiddle fails to load

* Warn and skip writing file if json fails to load

Author: rwstauner

harness/harness-common.rb

@@ -71,6 +71,9 @@ def get_maxrss
   raise unless result.zero?
   maxrss_kb = buffer[offset, Fiddle::SIZEOF_LONG].unpack1('q')
   1024 * maxrss_kb
+rescue LoadError
+  warn "Failed to get max RSS: #{$!.message}"
+  nil
 end
 
 # Do expand_path at require-time, not when returning results, before the benchmark is likely to chdir
@@ -87,22 +90,31 @@ def return_results(warmup_iterations, bench_iterations)
 
   # Collect our own peak mem usage as soon as reasonable after finishing the last iteration.
   rss = get_rss
-  maxrss = get_maxrss
-  puts "RSS: %.1fMiB" % (rss / 1024.0 / 1024.0)
-  puts "MAXRSS: %.1fMiB" % (maxrss / 1024.0 / 1024.0)
   yjit_bench_results["rss"] = rss
-  yjit_bench_results["maxrss"] = maxrss
+  puts "RSS: %.1fMiB" % (rss / 1024.0 / 1024.0)
+
+  if maxrss = get_maxrss
+    puts "MAXRSS: %.1fMiB" % (maxrss / 1024.0 / 1024.0)
+    yjit_bench_results["maxrss"] = maxrss
+  end
 
   if defined?(RubyVM::YJIT) && RubyVM::YJIT.stats_enabled?
     yjit_bench_results["yjit_stats"] = RubyVM::YJIT.runtime_stats
   end
 
+  write_json_file(yjit_bench_results)
+end
+
+def write_json_file(yjit_bench_results)
   require "json"
+
   out_path = YB_OUTPUT_FILE
   system('mkdir', '-p', File.dirname(out_path))
 
   # Using default path? Print where we put it.
   puts "Writing file #{out_path}" unless ENV["RESULT_JSON_PATH"]
 
   File.write(out_path, JSON.pretty_generate(yjit_bench_results))
+rescue LoadError
+  warn "Failed to write JSON file: #{$!.message}"
 end

harness/harness.rb

@@ -1,4 +1,3 @@
-require 'benchmark'
 require_relative "./harness-common"
 
 # Warmup iterations
@@ -19,14 +18,28 @@
 
 puts RUBY_DESCRIPTION
 
+if defined?(Process.clock_gettime) && defined?(Process::CLOCK_MONOTONIC)
+  def realtime
+    r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+    yield
+    Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
+  end
+else
+  require "benchmark"
+
+  def realtime(&block)
+    Benchmark.realtime(&block)
+  end
+end
+
 # Takes a block as input
-def run_benchmark(_num_itrs_hint)
+def run_benchmark(_num_itrs_hint, &block)
   times = []
   total_time = 0
   num_itrs = 0
 
   begin
-    time = Benchmark.realtime { yield }
+    time = realtime(&block)
     num_itrs += 1
 
     # NOTE: we may want to avoid this as it could trigger GC?