Understanding USDT Probes

USDT, or Userland Statically Defined Tracing, is a powerful tool that allows developers to trace and monitor the behavior of their applications without significant performance overhead. By embedding static probes into the code, you can gather valuable insights into how your application operates, enabling you to optimize and troubleshoot more effectively.

What are USDT Probes?

USDT probes are predefined points in your application’s code where you can insert special macros. These macros, when compiled, become triggers for the probe, allowing you to collect information about the application’s execution. The beauty of USDT is that these probes are static, meaning they are defined at compile time and can be activated or deactivated without recompiling the code.

How USDT Works

USDT operates by leveraging the SystemTap tool in Linux. When you compile your application with USDT probes, the compiler inserts the necessary code to enable or disable the probes. During runtime, you can use SystemTap to attach to these probes and collect data. This approach ensures that the probes have minimal impact on the application’s performance.

Using USDT Probes with eBPF

When it comes to performance analysis and fault diagnosis, eBPF (Extended Berkeley Packet Filter) is a powerful tool. USDT can provide valuable context information when used in conjunction with eBPF. By using USDT probes, you can track the number of times a specific function is called or collect stack trace information when an event occurs. This can be incredibly useful for understanding the behavior of your application and identifying potential bottlenecks.

How to Use BCC to View USDT Probes

Using BCC (BPF Compiler Collection) to view USDT probes is straightforward. You can use the following command to list all USDT probes in a program, including their names and locations:

sudo bcc usdt_list /path/to/program

This command will display all the USDT probes in the specified program, making it easier to identify and analyze the data collected by these probes.

Defining USDT Probes in Source Code

Defining USDT probes in your source code requires the use of special macros. For example, in a C or C++ application, you can use the DTRACEPROBE2 and DTRACEPROBE1 macros to define probes at the beginning and end of a function, respectively. Here’s an example of how you might define a USDT probe in a C program:

define DTRACEPROBE1(name, args) struct usdt_event e; usdt_event_init(name, args); usdt_event_print(e);void my_function(int arg1, float arg2) {    // Function code here;    DTRACEPROBE1("my_function", "ii", arg1, arg2);}void main() {    // <

 
 
			
			
 
						
		hmstr to usdt​