Green threads are much cheaper to switch than pthreads, yes. In real applications the difference is far smaller than it was 20 years ago when C10k was challengi

Green threads are much cheaper to switch than pthreads, yes. In real applications the difference is far smaller than it was 20 years ago when C10k was challenging. In 2020 you can just open 10k threads and forget about it. With 100k threads and 100k Goroutines, each doing nothing but waiting on a mutex: pthreads in C takes ~20 microseconds per thread and in Go it’s about ~5 microseconds using Goroutines. This difference disappears really easily. Parse some JSON and it’ll be gone. Entering kernel code is the expensive part of context switching so syscalls are very nearly as expensive. Reading from a socket still needs a syscall, even with green threads or asynchronous IO. The more different bits of IO you do, like in a real web app, the less advantage their is to green threads. This is one reason Rust dropped their M:N threading implementation.