We all love and use C++ because of its performance. But how do we actually measure the performance of an application? How do we check whether an application is CPU- or I/O bound? How do we see if our application is influenced by others running on the same system? There are many good and valid answers to these questions. Tracing certainly is a very valuable addition to everyone’s toolset. It can offer in-depth insights into what a system is doing and why an application is performing in a given way. Done properly, we can use it to piece together multiple pieces of the picture: How is our hardware utilized, what is the kernel doing, what is my application doing? In this talk, we will give an introduction to LTTng, a tracing toolkit for Linux, and show how it can be applied on embedded Linux systems to get an answer to the following question: What can I do to optimize the startup time of my application? We will talk about configuring Qt and LTTng properly. We will discuss the most useful kernel trace points and demonstrate the tracing subsystem in Qt for custom user space trace points. And we will look at how to analyze the collected data in a way that doesn’t make you want to pull your hair out. The contents of this talk stem from the experience of successfully optimizing automotive Qt applications on embedded Linux applications. The lessons learned apply to a much broader audience and can also be used with other tracing toolkits such as ETW on Windows.