Debug high CPU usage in .NET Core

In this tutorial, you‘ll learn how to debug an excessive CPU usage scenario. Using the provided example ASP.NET Core web app source code repository, you can cause a deadlock intentionally. The endpoint will experience a hang and thread accumulation. You‘ll learn how you can use various tools to diagnose this scenario with several key pieces of diagnostics data.

In this tutorial, you will:

Prerequisites

The tutorial uses:

• .NET Core 3.1 SDK or a later version.
• Sample debug target to trigger the scenario.
• dotnet-trace to list processes and generate a profile.
• dotnet-counters to monitor cpu usage.

CPU counters

Before attempting to collect diagnostics data, you need to observe a high CPU condition. Run the sample application using the following command from the project root directory.

dotnet run

To find the process ID, use the following command:

dotnet-trace ps

Take note of the process ID from your command output. Our process ID was 22884, but yours will be different. To check the current CPU usage, use the dotnet-counters tool command:

dotnet-counters monitor --refresh-interval 1 -p 22884

The refresh-interval is the number of seconds between the counter polling CPU values. The output should be similar to the following:

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

[System.Runtime]
    % Time in GC since last GC (%)                         0
    Allocation Rate / 1 sec (B)                            0
    CPU Usage (%)                                          0
    Exception Count / 1 sec                                0
    GC Heap Size (MB)                                      4
    Gen 0 GC Count / 60 sec                                0
    Gen 0 Size (B)                                         0
    Gen 1 GC Count / 60 sec                                0
    Gen 1 Size (B)                                         0
    Gen 2 GC Count / 60 sec                                0
    Gen 2 Size (B)                                         0
    LOH Size (B)                                           0
    Monitor Lock Contention Count / 1 sec                  0
    Number of Active Timers                                1
    Number of Assemblies Loaded                          140
    ThreadPool Completed Work Item Count / 1 sec           3
    ThreadPool Queue Length                                0
    ThreadPool Thread Count                                7
    Working Set (MB)                                      63

With the web app running, immediately after startup, the CPU isn‘t being consumed at all and is reported at 0%. Navigate to the api/diagscenario/highcpu route with 60000 as the route parameter:

https://localhost:5001/api/diagscenario/highcpu/60000

Now, rerun the dotnet-counters command. To monitor just the cpu-usage, specify System.Runtime[cpu-usage] as part of the command.

dotnet-counters monitor --counters System.Runtime[cpu-usage] -p 22884 --refresh-interval 1

You should see an increase in CPU usage as shown below:

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

[System.Runtime]
    CPU Usage (%)                                         25

Throughout the duration of the request, the CPU usage will hover around 25% . Depending on the host machine, expect varying CPU usage.

At this point, you can safely say the CPU is running higher than you expect.

Trace generation

When analyzing a slow request, you need a diagnostics tool that can provide insights into what the code is doing. The usual choice is a profiler, and there are different profiler options to choose from.

dotnet-trace collect -p 22884 --providers Microsoft-DotNETCore-SampleProfiler

CPU 问题 —— 数据收集（官网）-- Debug high CPU usage in .NET Core