Tutorial: Measure performance using EventCounters in .NET Core

Article
06/24/2023

This article applies to: ✔️ .NET Core 3.0 SDK and later versions

In this tutorial, you'll learn how an EventCounter can be used to measure performance with a high frequency of events. You can use the available counters published by various official .NET Core packages, third-party providers, or create your own metrics for monitoring.

In this tutorial, you will:

Implement an EventSource.
Monitor counters with dotnet-counters.

Prerequisites

The tutorial uses:

.NET Core 3.1 SDK or a later version.
dotnet-counters to monitor event counters.
A sample debug target app to diagnose.

Get the source

The sample application will be used as a basis for monitoring. The sample ASP.NET Core repository is available from the samples browser. You download the zip file, extract it once downloaded, and open it in your favorite IDE. Build and run the application to ensure that it works properly, then stop the application.

Implement an EventSource

For events that happen every few milliseconds, you'll want the overhead per event to be low (less than a millisecond). Otherwise, the impact on performance will be significant. Logging an event means you're going to write something to disk. If the disk is not fast enough, you will lose events. You need a solution other than logging the event itself.

When dealing with a large number of events, knowing the measure per event is not useful either. Most of the time all you need is just some statistics out of it. So you could get the statistics within the process itself and then write an event once in a while to report the statistics, that's what EventCounter will do.

Below is an example of how to implement an System.Diagnostics.Tracing.EventSource. Create a new file named MinimalEventCounterSource.cs and use the code snippet as its source:

using System.Diagnostics.Tracing;

[EventSource(Name = "Sample.EventCounter.Minimal")]
public sealed class MinimalEventCounterSource : EventSource
{
    public static readonly MinimalEventCounterSource Log = new MinimalEventCounterSource();

    private EventCounter _requestCounter;

    private MinimalEventCounterSource() =>
        _requestCounter = new EventCounter("request-time", this)
        {
            DisplayName = "Request Processing Time",
            DisplayUnits = "ms"
        };

    public void Request(string url, long elapsedMilliseconds)
    {
        WriteEvent(1, url, elapsedMilliseconds);
        _requestCounter?.WriteMetric(elapsedMilliseconds);
    }

    protected override void Dispose(bool disposing)
    {
        _requestCounter?.Dispose();
        _requestCounter = null;

        base.Dispose(disposing);
    }
}

The EventSource.WriteEvent line is the EventSource part and is not part of EventCounter, it was written to show that you can log a message together with the event counter.

Add an action filter

The sample source code is an ASP.NET Core project. You can add an action filter globally that will log the total request time. Create a new file named LogRequestTimeFilterAttribute.cs, and use the following code:

using System.Diagnostics;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.Mvc.Filters;

namespace DiagnosticScenarios
{
    public class LogRequestTimeFilterAttribute : ActionFilterAttribute
    {
        readonly Stopwatch _stopwatch = new Stopwatch();

        public override void OnActionExecuting(ActionExecutingContext context) => _stopwatch.Start();

        public override void OnActionExecuted(ActionExecutedContext context)
        {
            _stopwatch.Stop();

            MinimalEventCounterSource.Log.Request(
                context.HttpContext.Request.GetDisplayUrl(), _stopwatch.ElapsedMilliseconds);
        }
    }
}

The action filter starts a Stopwatch as the request begins, and stops after it has been completed, capturing the elapsed time. The total milliseconds are logged to the MinimalEventCounterSource singleton instance. For this filter to be applied, you need to add it to the filter collection. In the Startup.cs file, update the ConfigureServices method in include this filter.

public void ConfigureServices(IServiceCollection services) =>
    services.AddControllers(options => options.Filters.Add<LogRequestTimeFilterAttribute>())
            .AddNewtonsoftJson();

Monitor event counter

With the implementation on an EventSource and the custom action filter, build and launch the application. You logged the metric to the EventCounter, but unless you access the statistics from of it, it is not useful. To get the statistics, you need to enable the EventCounter by creating a timer that fires as frequently as you want the events, as well as a listener to capture the events. To do that, you can use dotnet-counters.

Use the dotnet-counters ps command to display a list of .NET processes that can be monitored.

dotnet-counters ps

Using the process identifier from the output of the dotnet-counters ps command, you can start monitoring the event counter with the following dotnet-counters monitor command:

dotnet-counters monitor --process-id 2196 --counters Sample.EventCounter.Minimal,Microsoft.AspNetCore.Hosting[total-requests,requests-per-second],System.Runtime[cpu-usage]

While the dotnet-counters monitor command is running, hold F5 on the browser to start issuing continuous requests to the https://localhost:5001/api/values endpoint. After a few seconds stop by pressing q

Press p to pause, r to resume, q to quit.
    Status: Running

[Microsoft.AspNetCore.Hosting]
    Request Rate / 1 sec                               9
    Total Requests                                   134
[System.Runtime]
    CPU Usage (%)                                     13
[Sample.EventCounter.Minimal]
    Request Processing Time (ms)                      34.5

The dotnet-counters monitor command is great for active monitoring. However, you may want to collect these diagnostic metrics for post processing and analysis. For that, use the dotnet-counters collect command. The collect switch command is similar to the monitor command, but accepts a few additional parameters. You can specify the desired output file name and format. For a JSON file named diagnostics.json use the following command:

dotnet-counters collect --process-id 2196 --format json -o diagnostics.json --counters Sample.EventCounter.Minimal,Microsoft.AspNetCore.Hosting[total-requests,requests-per-second],System.Runtime[cpu-usage]

Again, while the command is running, hold F5 on the browser to start issuing continuous requests to the https://localhost:5001/api/values endpoint. After a few seconds stop by pressing q. The diagnostics.json file is written. The JSON file that is written is not indented, however; for readability it is indented here.

{
  "TargetProcess": "DiagnosticScenarios",
  "StartTime": "8/5/2020 3:02:45 PM",
  "Events": [
    {
      "timestamp": "2020-08-05 15:02:47Z",
      "provider": "System.Runtime",
      "name": "CPU Usage (%)",
      "counterType": "Metric",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:47Z",
      "provider": "Microsoft.AspNetCore.Hosting",
      "name": "Request Rate / 1 sec",
      "counterType": "Rate",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:47Z",
      "provider": "Microsoft.AspNetCore.Hosting",
      "name": "Total Requests",
      "counterType": "Metric",
      "value": 134
    },
    {
      "timestamp": "2020-08-05 15:02:47Z",
      "provider": "Sample.EventCounter.Minimal",
      "name": "Request Processing Time (ms)",
      "counterType": "Metric",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:47Z",
      "provider": "System.Runtime",
      "name": "CPU Usage (%)",
      "counterType": "Metric",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:48Z",
      "provider": "Microsoft.AspNetCore.Hosting",
      "name": "Request Rate / 1 sec",
      "counterType": "Rate",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:48Z",
      "provider": "Microsoft.AspNetCore.Hosting",
      "name": "Total Requests",
      "counterType": "Metric",
      "value": 134
    },
    {
      "timestamp": "2020-08-05 15:02:48Z",
      "provider": "Sample.EventCounter.Minimal",
      "name": "Request Processing Time (ms)",
      "counterType": "Metric",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:48Z",
      "provider": "System.Runtime",
      "name": "CPU Usage (%)",
      "counterType": "Metric",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:50Z",
      "provider": "Microsoft.AspNetCore.Hosting",
      "name": "Request Rate / 1 sec",
      "counterType": "Rate",
      "value": 0
    },
    {
      "timestamp": "2020-08-05 15:02:50Z",
      "provider": "Microsoft.AspNetCore.Hosting",
      "name": "Total Requests",
      "counterType": "Metric",
      "value": 134
    },
    {
      "timestamp": "2020-08-05 15:02:50Z",
      "provider": "Sample.EventCounter.Minimal",
      "name": "Request Processing Time (ms)",
      "counterType": "Metric",
      "value": 0
    }
  ]
}

Next steps

EventCounters

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