DevTalks: Profile .Net apps with Windows Performance Toolkit

From time to time any developer faces performance problems. In fact we've got 2 problems: how to find bottleneck and how to fix it. In this article I'll try to give an answer to the first question.

Introduction

Windows Performance Toolkit (WPT) is a set of tools for analyzing performance problems. It's built on top of Event Trace for Windows (ETW). ETW is an unified mechanism for tracing on Windows platform. WPT helps us capture ETW events which were produced by ETW providers. All Windows components have ETW providers. For instance, here you can read about CLR ETW provider.

You can download WPT here.

Windows Performance Recorder

Windows Performance Recorder is GUI tool for capturing tracing events. These tracing events are stored in ETL tracing file. After installation you can find WprUI in this folder: C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\WPRUI.exe. This is default path on my Windows 8.1. Here how it looks like.

Windows Performance Recorder

Windows Performance Analyzer

Windows Performance Analyzer is GUI tool for analyzing ETL trace files. After installation you can find WPA here: C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\WPA.exe.

Windows Performance Analyzer

'Graph explorer' panel contains hierarchy of predefined graphs which we can use for analyzing performance of the system. In Computation node you can find all CPU related graphs. On the screenshot above 'CPU Usage (Sampled)' was selected. This graph is build using sample profile interrupt. This interrupt every millisecond gathers call stack from all CPUs.

Profiling

In order to find performance issues in an app we should follow this algorithm:

  1. Run WPR and start tracing
  2. Run the app
  3. Stop tracing and save events on disk
  4. Analyze etl file in WPA.
Run WPR

Before pressing 'Start' button in WprUI we should choose which profiles we want to listen. We are interested in CPU investigation this is why we should tick: 'First level triage' (enables common ETW providers) and 'CPU usage'. Now we can click 'Start' button.

Analyze etl file in WPA.

When the app is finished we can click 'Save' button in WPR. It takes some time for WPR to prepare etl file for analyzing. After that we can open etl file in WPA by click 'Open in WPA' button.

Example

Below you can see 'CPU Usage (Sampled)' graph which shows CpuTest app.

CpuTest App

If you right click on the table header you will see a list of additional columns. Select Stack to see callstacks. Don't forget to load symbols (Trace -> Load Symbols).

CpuTest is very simple app. It consists of 3 methods: Main, CalculateExpression and CreateUser. Main calls CalculateExpression and CreateUser. As you see on the screenshot most of the time we spent in CalculateExpression (23833 samples) compare to CreateUser (7933 samples). Now we know the method which consume most of the CPU and can start fixing it.

Cheers