Understanding eBPF and USDT

When it comes to performance analysis and debugging, the combination of Extended Berkeley Packet Filter (eBPF) and Userland Statically Defined Tracing (USDT) can be a powerful tool. In this article, we will delve into what eBPF and USDT are, how they work together, and how you can leverage this technology to gain deeper insights into your applications.

What is eBPF?

eBPF is a technology that allows you to run code in the Linux kernel. It was originally developed by the Linux Foundation and is now widely used for various purposes, including network packet filtering, security, and performance monitoring. eBPF programs are written in a low-level language and can be attached to various kernel hooks, allowing you to inspect and manipulate the kernel’s behavior.

What is USDT?

USDT is a user-space tracing technology that was introduced by the Solaris operating system. It allows developers to define static probe points in their applications, which can be dynamically attached by tracing tools to collect information. These probe points are predefined in the code and are disabled by default, only becoming active when a tracing tool is attached to them. This approach minimizes the impact on application performance while providing rich dynamic tracing and diagnostic information.

How eBPF and USDT Work Together

The combination of eBPF and USDT can be particularly useful for performance analysis and debugging. eBPF provides the kernel-side capabilities, while USDT offers the user-space context. Here’s how they work together:

By combining the strengths of both technologies, you can gain a comprehensive view of your application’s performance and behavior. For example, you can use eBPF to monitor network traffic and identify potential bottlenecks, while USDT can provide detailed information about the application’s execution, such as the number of times a specific function was called and the stack trace at the time of an error.

Using USDT Probes with eBPF

One way to leverage USDT with eBPF is by using BCC (BPF Compiler Collection), a toolkit that provides a high-level interface for writing eBPF programs. To view USDT probes in a BCC program, you can use the following command:

bcc probe usdt -p  -m  -n 

This command will list all USDT probes in the specified process, including the probe name and location. To define static probe points in your application, you need to add special macros to your source code. These macros will be expanded during compilation to insert the code that triggers the probe. Here’s an example of how to define a USDT probe in a C program:

include DTRACEPROBE2(int, my_probe, int, arg1, int, arg2){    // Code to be executed when the probe is triggered    printf("Probe triggered with arg1: %d and arg2: %d", arg1, arg2);}

In this example, DTRACEPROBE2 is a macro that defines a USDT probe. When the probe is triggered, it will print the values of the arguments passed to the probe.

Conclusion

By combining eBPF and USDT, you can gain a deeper understanding of your application’s performance and behavior. This powerful combination allows you to monitor both kernel and user-space aspects of your application, providing valuable insights for debugging and optimization. Whether you’re a developer or a system administrator, leveraging this technology can help you identify and resolve issues more efficiently.