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 BCC

BCC (BPF Compiler Collection) is a popular eBPF toolkit that provides a convenient way to work with USDT probes. To view the USDT probes in a program, you can use the following command:

bcc usdt probe list

This command will list all the USDT probes in the program, including their names and locations. 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. When the probe is activated, it will collect and record useful information related to the program’s execution.

Example: Defining USDT Probes in a C Program

In this example, we will demonstrate how to define USDT probes in a C program using the DTrace and SystemTap APIs:

include include int main() {    DTRACE_PROBE2("myapp", "entry", "int", arg1, "int", arg2);    printf("Function entry with args: %d, %d", arg1, arg2);    DTRACE_PROBE2("myapp", "exit", "int", arg1, "int", arg2);    printf("Function exit with args: %d, %d", arg1, arg2);    return 0;}

In this code, we define two USDT probes: one for the function entry and another for the function exit. The DTRACE_PROBE2 macro is used to create the probe points, and the printf statements are used to display the arguments passed to the function.

Conclusion

The combination of eBPF and USDT offers a powerful solution for performance analysis and debugging. By leveraging the strengths of both technologies, you can gain a deeper understanding of your application’s behavior and identify potential issues more efficiently. Whether you are a developer or a system administrator, mastering eBPF and USDT can help you optimize your applications and