benchmark,lib: add process.hrtime.bigint benchmark

Add a benchmark, and amend the relevant source code comment to state
that currently, switching to directly returning a BigInt is not
stopped by technical obstacles but rather the fact that using a typed
array is actually a bit faster (about 2.5 %, measured locally).

PR-URL: https://github.com/nodejs/node/pull/26381
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

benchmark/process/bench-hrtime.js

@@ -5,27 +5,38 @@ const assert = require('assert');
 
 const bench = common.createBenchmark(main, {
   n: [1e6],
-  type: ['raw', 'diff']
+  type: ['raw', 'diff', 'bigint']
 });
 
 function main({ n, type }) {
   const hrtime = process.hrtime;
-  var noDead = hrtime();
+  var noDead = type === 'bigint' ? hrtime.bigint() : hrtime();
   var i;
 
-  if (type === 'raw') {
-    bench.start();
-    for (i = 0; i < n; i++) {
-      noDead = hrtime();
-    }
-    bench.end(n);
-  } else {
-    bench.start();
-    for (i = 0; i < n; i++) {
-      noDead = hrtime(noDead);
-    }
-    bench.end(n);
+  switch (type) {
+    case 'raw':
+      bench.start();
+      for (i = 0; i < n; i++) {
+        noDead = hrtime();
+      }
+      bench.end(n);
+      break;
+    case 'diff':
+      bench.start();
+      for (i = 0; i < n; i++) {
+        noDead = hrtime(noDead);
+      }
+      bench.end(n);
+      break;
+    case 'bigint':
+      bench.start();
+      for (i = 0; i < n; i++) {
+        noDead = hrtime.bigint();
+      }
+      bench.end(n);
+      break;
   }
 
-  assert.ok(Array.isArray(noDead));
+  // eslint-disable-next-line valid-typeof
+  assert.ok(Array.isArray(noDead) || typeof noDead === 'bigint');
 }

lib/internal/process/per_thread.js

@@ -120,8 +120,8 @@ function setupHrtime(_hrtime, _hrtimeBigInt) {
     ];
   };
 
-  // Use a BigUint64Array in the closure because V8 does not have an API for
-  // creating a BigInt out of a uint64_t yet.
+  // Use a BigUint64Array in the closure because this is actually a bit
+  // faster than simply returning a BigInt from C++ in V8 7.1.
   const hrBigintValues = new BigUint64Array(1);
   process.hrtime.bigint = function() {
     _hrtimeBigInt(hrBigintValues);