Why Does My cgo Code Run Slower Than Pure Go?

Why cgo Underperforms: Understanding the Overhead of Interfacing with C

In your performance test comparing cgo functions and pure Go functions, you observed that the cgo function took longer to execute, leaving you perplexed. Let's investigate the underlying reasons for this performance disparity.

As you have noticed, cgo invokes external C code, which introduces several layers of overhead. To minimize this overhead, it is recommended to limit cgo calls as much as possible. In your example, instead of repeating cgo calls within a loop, it would be more efficient to migrate the loop into the C function.

However, the architectural differences between C and Go's execution models contribute to cgo's performance limitations.

Go's runtime manages thread execution differently from C, leading to potential compatibility issues:

• Goroutines utilize limited stack space and employ segmented stacks or copying mechanisms to handle stack expansion.
• Thread Local Storage (TLS) implementations in C's libpthread may conflict with Go's runtime.
• Go's UNIX signal handler can disrupt C code execution.
• Goroutines are multiplexed onto OS threads, so if C code blocks or monopolizes the thread, it can impact other goroutines.

To address these concerns, cgo operates within a separate thread equipped with a traditional stack, ensuring compatibility.

While cgo can be beneficial for integrating pre-existing libraries, it is crucial to use it judiciously. Instead of relying on cgo for performance improvements, prioritize implementing performance-sensitive segments in Go itself.

By understanding these complexities, you can optimize your cgo usage and strike a balance between performance and interoperability.

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