How do blocking system calls affect the scheduler?

In Go, the scheduler manages the distribution of goroutines across system threads (M). When a blocking system call occurs (for example, reading from a file or network operation), the thread executing the goroutine becomes blocked.

If the blocking call is not handled properly, it can lead to decreased performance, as the scheduler cannot efficiently utilize this thread to run other goroutines.

However, the Go runtime has a mechanism: upon detecting a blocking system call, the scheduler can create an additional thread to compensate for the blocked one and continue executing other goroutines. This helps minimize the impact of blocking on parallelism.

Nevertheless, if there are many such blocks or they last long, it can lead to an increase in the number of threads and overhead from context switching, which negatively affects performance.

Thus, blocking system calls can slow down the scheduler, but the Go runtime tries to minimize this effect by creating additional threads when necessary.