Why is CGo Slower Than Pure Go, and How Can I Improve Performance?

Performance Drawbacks of CGo Calls

Your observation of the slower performance of the Cgo function compared to the pure Go function aligns with the inherent overheads of invoking C/C code via CGo. To mitigate this performance gap, minimizing the frequency of CGo calls is crucial. Consider relocating the loop to C to avoid repetitive CGo calls.

Consequences of Go Runtime Threading for C Code

Additionally, the Go runtime's threading setup can impact the performance of C code. Here are some notable aspects:

• Goroutines utilize small stacks, employing segmented stacks or copying mechanisms for stack growth.
• Threads initiated by the Go runtime may face compatibility issues with the thread-local storage implementation of libpthread.
• The UNIX signal handler employed by the Go runtime can potentially disrupt traditional C or C code.
• Go's reuse of OS threads to execute multiple Goroutines can hinder the performance of C code if blocking system calls or monopolization of threads occurs.

CGo's Safety-Oriented Approach

Due to these factors, CGo opts for a conservative approach, executing C code in a dedicated thread with a conventional stack.

Performance Expectations in Go

In contrast to languages like Python, where rewriting performance-critical sections in C is a common practice, the performance gap between equivalent C and Go code is significantly narrower. Consequently, CGo is typically reserved for interfacing with existing libraries, potentially supported by small C wrapper functions to reduce CGo call frequency.

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