perf_hooks: implement histogram based api

Add a sampling-based event loop delay monitor.

```js
const { monitorEventLoopDelay } = require('perf_hooks');

const h = monitorEventLoopDelay();

h.enable();

h.disable();

console.log(h.percentiles);
console.log(h.min);
console.log(h.max);
console.log(h.mean);
console.log(h.stddev);
console.log(h.percentile(50));
```

PR-URL: https://github.com/nodejs/node/pull/25378
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

1 files changed, 113 insertions, 0 deletions

diff --git a/doc/api/perf_hooks.md b/doc/api/perf_hooks.md
index a891e875b5..d805a0cf9d 100644
--- a/doc/api/perf_hooks.md
+++ b/doc/api/perf_hooks.md
@@ -398,6 +398,119 @@ Returns a list of `PerformanceEntry` objects in chronological order
 with respect to `performanceEntry.startTime` whose `performanceEntry.entryType`
 is equal to `type`.
 
+## monitorEventLoopDelay([options])
+<!-- YAML
+added: REPLACEME
+-->
+
+* `options` {Object}
+  * `resolution` {number} The sampling rate in milliseconds. Must be greater
+    than zero. Defaults to `10`.
+* Returns: {Histogram}
+
+Creates a `Histogram` object that samples and reports the event loop delay
+over time.
+
+Using a timer to detect approximate event loop delay works because the
+execution of timers is tied specifically to the lifecycle of the libuv
+event loop. That is, a delay in the loop will cause a delay in the execution
+of the timer, and those delays are specifically what this API is intended to
+detect.
+
+```js
+const { monitorEventLoopDelay } = require('perf_hooks');
+const h = monitorEventLoopDelay({ resolution: 20 });
+h.enable();
+// Do something
+h.disable();
+console.log(h.min);
+console.log(h.max);
+console.log(h.mean);
+console.log(h.stddev);
+console.log(h.percentiles);
+console.log(h.percentile(50));
+console.log(h.percentile(99));
+```
+
+### Class: Histogram
+<!-- YAML
+added: REPLACEME
+-->
+Tracks the event loop delay at a given sampling rate.
+
+#### histogram.disable()
+<!-- YAML
+added: REPLACEME
+-->
+
+* Returns: {boolean}
+
+Disables the event loop delay sample timer. Returns `true` if the timer was
+stopped, `false` if it was already stopped.
+
+#### histogram.enable()
+<!-- YAML
+added: REPLACEME
+-->
+
+* Returns: {boolean}
+
+Enables the event loop delay sample timer. Returns `true` if the timer was
+started, `false` if it was already started.
+
+#### histogram.exceeds
+
+* Value: {number}
+
+The number of times the event loop delay exceeded the maximum 1 hour event
+loop delay threshold.
+
+#### histogram.max
+
+* Value: {number}
+
+The maximum recorded event loop delay.
+
+#### histogram.mean
+
+* Value: {number}
+
+The mean of the recorded event loop delays.
+
+#### histogram.min
+<!-- YAML
+added: REPLACEME
+-->
+
+* Value: {number}
+
+The minimum recorded event loop delay.
+
+#### histogram.percentile(percentile)
+
+* `percentile` {number} A percentile value between 1 and 100.
+
+Returns the value at the given percentile.
+
+#### histogram.percentiles
+
+* Value: {Map}
+
+Returns a `Map` object detailing the accumulated percentile distribution.
+
+#### histogram.reset()
+<!-- YAML
+added: REPLACEME
+-->
+
+Resets the collected histogram data.
+
+#### histogram.stddev
+
+* Value: {number}
+
+The standard deviation of the recorded event loop delays.
+
 ## Examples
 
 ### Measuring the duration of async operations