Comment by mixedbit

gVisor has performance benchmarks: https://gvisor.dev/docs/architecture_guide/performance/ Long ago I worked on and benchmarked a Linux user space virtual filesystem that used ptrace to intercept and amend system calls. For surprisingly many workloads, per system call performance overhead is negligible. This is because many programs either wait for IO, in which case the small added overhead of a system call doesn't really matter, or spend time on CPU doing some computation. Only workloads where kernel is hit with long series of syscalls have measurable performance overhead. The difference is visible in benchmarks, but not anything that a user is able to notice in an interactive shell session.