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Hands-On High Performance Programming with Qt 5
Hands-On High Performance Programming with Qt 5

Hands-On High Performance Programming with Qt 5: Build cross-platform applications using concurrency, parallel programming, and memory management

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Hands-On High Performance Programming with Qt 5

Profiling to Find Bottlenecks

As we already described in Chapter 1, Understanding Performant Programs, performance bottlenecks are not distributed evenly in code. Applying the Pareto principle to performance optimization, we could say that 80% of a program's execution time is spent on 20% of the code (and, as we've seen, Donald Knuth believed this to be an even lower figure). Regardless of the exact proportions, the basic insight is the same—code optimization efforts are most effectively spent on that critical x percent of the code that is responsible for most of the program's execution time.

We saw in the previous chapter that today's hardware platforms have grown to be so complicated that the ancient adage about programmers being notoriously bad at estimating bottlenecks in their own code has now been reinforced more than ever—not only do we...

Types of profilers

The problem is, as we mentioned, we don't know what the program, the operating system or the hardware are exactly doing, and how much time each of them needs. So, we have to obtain this information somehow. The process of doing so is called profiling (creating the program's execution profile), and the tools we use to do that are called profilers. There are the following general approaches used to obtain performance data:

  • Program instrumentation
  • Runtime sampling
  • Reading hardware or operating system counters

Let's look at each of these approaches in more detail.

Instrumenting profilers

Code instrumentation means adding additional code to our existing code base that will measure performance...

Platform and tools

Now, as we already know what kinds of tools can be used for profiling, there will come a time when we will have to get our hands dirty and delve deeper into typical performance optimization work. For you to be able to reproduce it, we have to agree on the exact versions of our frameworks and tools. To make it short, we've decided on the following:

  • Qt 5.9 LTE
  • Windows 10
  • Open source tools

This warrants some explanation, so read on. Let's start with the Qt framework.

Qt has many different versions and releases, but in this book, we have chosen to concentrate on the current (at the time of writing) long-term support (LTS) version, namely Qt 5.9—as it's the recent most stable release. Admittedly, a preview version of Qt 5.11 was present in the distribution, but we have, much to my regret, to ignore it.

Qt is a multiplatform framework; it...

Profiling CPU usage

On Linux Qt, Creator integrates with Valgrind's callgrind, which, alas, isn't available on Windows, so we have to look for other tools. Before we jump to the dedicated tools, let's discuss a very basic, little-known (as far as I can judge), but surprisingly effective, technique.

Poor man's sampling technique

I call that technique the poor man's sampling technique. It is really simple. In its most basic form, you run a program in a debugger, stop it several times, and examine the call stack of the randomly chosen breaks. The idea is (as with sampling profilers) that the most-used function will show most often in the stack trace. Simple as it is, this quick technique will sometimes...

Investigating memory usage

On Linux Qt, Creator integrates with Valgrind's memcheck, which, alas, isn't available on Windows, so we have to look for other tools. Before we jump into dedicated tools, however, let's first have a look at Windows system tools.

Poor man's memory profiling

Unexpectedly, sometimes, much can be done just by using the old and trusty Process Explorer tool we introduced in the Widows system tools section earlier in this chapter. Let's discuss this with a real-life example.

In a project for one of my customers, there was a Qt application that suffered from timeouts when fetching frames from a camera. This is arguably a performance problem, so I started an investigation. As a first...

Manual instrumentation and benchmarks

Is there too much complicated tooling for your taste? Don't panic; it doesn't always have to be a profiler; there is a set of simpler techniques, which oftentimes can prove to be quite sufficient.

Debug outputs

Sometimes, the simplest thing we can do is just to add some printfs reporting times spend in critical parts of the code as debug outputs (that is, they will disappear in your Release build). This is the simplest form of manual instrumentation we can have—no sophisticated output formats; just simple human-readable log lines.

We can use it in two ways: first, when investigating some incumbent performance problem, and, second, for an overview of the general timing...

Further advanced tools

Besides the basic performance tools introduced so far, there are many more specialized tools we can use. We will introduce some of them in detail and only briefly mention some others.

Event Tracing for Windows (ETW) and xperf

On Linux, we have the excellent and widely known perftools suite for reading any imaginable kernel counters that might be relevant for performance. A little less well-known is the fact that Windows sports an equally excellent free performance toolset, namely the ETW and xperf tools, also known as the Windows Performance Toolkit (WPT). ETW traces can show the total system behavior, and that is how different processes influence themselves. We can use it in more difficult performance...

Summary

So, there was an awful lot of tools in this chapter, and then some more. What did we really learn from this chapter, besides a litany of tool names? Although it doesn't look like this at first glance, we indeed learned several important things, namely the following:

  • What kinds of tools are programmers using for performance analysis?
  • What platform, Qt version, and development environment will we be relying on in this book?
  • What open source and free tools can we use on Windows in addition to Qt Creator?
  • Much insight can be gained by relatively simple means.
  • How to profile a QML application's CPU usage.
  • How to profile a C++ (and mixed QML/C++) application's CPU usage.
  • How to investigate memory usage and find memory leaks.

There are even more specialized performance tools you could use, so there's virtually no limit to the amount of data you can collect...

Questions

Here are some questions so that you can test your understanding of the topics in this chapter:

  1. What does this mean: Apitrace preloads an instrumented implementation of OpenGL? Explain.
  2. Isn't there a way to use the gprof after all?
  3. How would you look for a lock convoy or a waiting chain causing your UI to stutter or, even worse, to freeze?
  4. What is the difference between CPU Usage (Precise) and CPU Usage (Sampled) in ETW traces?
  1. How would you find timers running amok or QML items accumulating video memory?
  2. What can you do when your favorite open source performance is not supported by Qt Creator?
  3. What is that thread and lock analysis feature some of the tools seem to have?
  4. If you try to launch the example program directly or from an external CPU profiler, this won't work. Why not? How do you fix it?
  5. If we don't use any custom ETW events in our program...
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Key benefits

  • Build efficient and concurrent applications in Qt to create cross-platform applications
  • Identify performance bottlenecks and apply the correct algorithm to improve application performance
  • Delve into parallel programming and memory management to optimize your code

Description

Achieving efficient code through performance tuning is one of the key challenges faced by many programmers. This book looks at Qt programming from a performance perspective. You'll explore the performance problems encountered when using the Qt framework and means and ways to resolve them and optimize performance. The book highlights performance improvements and new features released in Qt 5.9, Qt 5.11, and 5.12 (LTE). You'll master general computer performance best practices and tools, which can help you identify the reasons behind low performance, and the most common performance pitfalls experienced when using the Qt framework. In the following chapters, you’ll explore multithreading and asynchronous programming with C++ and Qt and learn the importance and efficient use of data structures. You'll also get the opportunity to work through techniques such as memory management and design guidelines, which are essential to improve application performance. Comprehensive sections that cover all these concepts will prepare you for gaining hands-on experience of some of Qt's most exciting application fields - the mobile and embedded development domains. By the end of this book, you'll be ready to build Qt applications that are more efficient, concurrent, and performance-oriented in nature

Who is this book for?

This book is designed for Qt developers who wish to build highly performance applications for desktop and embedded devices. Programming Experience with C++ is required.

What you will learn

  • Understand classic performance best practices
  • Get to grips with modern hardware architecture and its performance impact
  • Implement tools and procedures used in performance optimization
  • Grasp Qt-specific work techniques for graphical user interface (GUI) and platform programming
  • Make Transmission Control Protocol (TCP) and Hypertext Transfer Protocol (HTTP) performant and use the relevant Qt classes
  • Discover the improvements Qt 5.9 (and the upcoming versions) holds in store
  • Explore Qt s graphic engine architecture, strengths, and weaknesses

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Publication date : Jan 31, 2019
Length: 384 pages
Edition : 1st
Language : English
ISBN-13 : 9781789533309
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Product Details

Publication date : Jan 31, 2019
Length: 384 pages
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Language : English
ISBN-13 : 9781789533309
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Table of Contents

13 Chapters
Understanding Performant Programs Chevron down icon Chevron up icon
Profiling to Find Bottlenecks Chevron down icon Chevron up icon
Deep Dive into C++ and Performance Chevron down icon Chevron up icon
Using Data Structures and Algorithms Efficiently Chevron down icon Chevron up icon
An In-Depth Guide to Concurrency and Multithreading Chevron down icon Chevron up icon
Performance Failures and How to Overcome Them Chevron down icon Chevron up icon
Understanding I/O Performance and Overcoming Related Problems Chevron down icon Chevron up icon
Optimizing Graphical Performance Chevron down icon Chevron up icon
Optimizing Network Performance Chevron down icon Chevron up icon
Qt Performance on Embedded and Mobile Platforms Chevron down icon Chevron up icon
Testing and Deploying Qt Applications Chevron down icon Chevron up icon
Assessments Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Full star icon Full star icon 5
(2 Ratings)
5 star 100%
4 star 0%
3 star 0%
2 star 0%
1 star 0%
sanghyun Dec 12, 2023
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Simply a great book on performance!
Subscriber review Packt
Roman Apr 29, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
The book is virtually the only book book on Qt performance at this point in time, and it does its job exceptionally well, It gives you an insight on existing tools and how to use them, on existing techniques and how to apply them, and on the various aspects of performance from a C++ perspective, as you can't really talk about Qt performance without talking about C++ performance. I consider myself a seasoned Qt and C++ developer, but I had a lot to learn from this book, and I would definitely recommend it to anyone dealing with Qt, the book really covers a lot.Another thing, which is not less important, is that the book is written really well, it is easy to read, and to understand.That being said - I noticed a few typos (not many though), the book is more Windows oriented (but many important Linux specific topics are also in the book), and I skipped almost everything related to QML, but this is not enough to detract a star from the ratings, so here we go.Very highly recommended.
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