Using C code to use cgo in Go does indeed bring performance overhead, which is mainly reflected in three aspects. First, every time a C function is called from Go, it needs to cross the boundaries of the execution model, involving context switching, which is hundreds to thousands of times slower than ordinary Go function calls, so it should be processed in batches or reduced frequently. Secondly, when data is passed between Go and C, it needs to be manually managed and copied, which increases runtime overhead and error possibility, and minimizes type conversion; finally, cgo calls will block operating system threads, affecting the efficiency of the Go scheduler, especially in high concurrency scenarios, which may lead to thread bloating. It is recommended to limit the number of concurrent Cgo calls or use resource pools and other technologies to alleviate the impact.
Using C code in Go via cgo comes with a performance cost, and while it's not always prohibitive, it's worth understanding where those costs come from and when they matter.

The Overhead of Crossing the C/Go Boundary
Every time your Go code calls into C (using C.function()
), there's a boundary crossing involved. This isn't just a simple function call—it involves switching from the Go execution model to the C one.

- Go has its own stack management and goroutine scheduling.
- Cassumes a fixed stack and uses the OS thread directly.
So when you make a cgo call:
- The current goroutine must stop.
- The OS thread must switch context into C mode.
- After the C call completes, it switches back to Go mode.
This transition is more expensive than a regular Go function call—often by orders of magnitude. For example, calling a simple C function like sqrt()
through cgo can be hundreds or even thousands of times slower than doing the same math in pure Go.

If you're making frequent small C calls in a loop, this overhead adds up fast. Try to batch operations or move more logic into C if possible.
Memory Management Adds Complexity
When passing data between Go and C, you often need to copy memory or manage points manually. This introduces two types of overhead:
- Data copying : Strings or byte slices passed to C must usually be copied because C expects NUL-terminated strings and doesn't understand Go's string representation.
- Manual memory management : You have to remember to free memory allocated in C using
C.free
, which can be error-prone.
For example, converting a Go string to a C string looks like this:
cStr := C.CString(goStr) defer C.free(unsafe.Pointer(cStr))
That extra step means more code, more potential for bugs, and some runtime overhead too.
Avoid frequent conversions. If you're dealing with large buffers or high-frequency calls, consider minimizing the number of transitions and keeping data on the C side as much as possible.
Impact on Concurrency and Scheduling
Because cgo calls block the OS thread they're running on, they can affect Go's scheduler behavior. Normally, goroutines are multiplexed onto fewer OS threads, but cgo changes that.
If many goroutines are blocked on cgo calls:
- Go may spin up additional threads to keep other goroutines running.
- That increases resource usage and scheduling complexity.
This is especially noticeable in highly concurrent programs like web servers. If each request makes a cgo call, you might see higher latency or increased memory use due to thread proliferation.
Limit how many concurrent cgo calls your app makes. Consider rate limiting or pooling techniques if you rely heavily on cgo-based libraries.
Basically, cgo is useful when needed, but not free. The main costs are boundary crossing overhead, memory handling, and concurrency impact. It's fine for occasional use, but not ideal for tight loops or high-throughput paths.
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