This might be true for your system and libc, where the system calls make use of things like vDSO for gettimeofday go fast, but in general this isn't guaranteed at all. Even on x64, for certain libc implementations, like musl, if I recall correctly, syscalls are made the old fashioned way by trapping 0x80, which would mean you would see a much bigger effect by reducing the number of syscalls.
There is no vDSO for calls to stat(2). The claim in the article was that by setting the TZ environment variable to ":/etc/localtime", one could save "thousands" of stat system calls. Even for old-fashioned system calls where you use trap 0x80, Linux is still amazingly fast.
This can actually be a problem, since there are applications like git which assume stat is fast, and so it aggressively stat's all of the working files in the repository to check the mod times to see if anything has changed. That's fine on Linux, but it's a disaster on Windows, where the stat system call is dog-slow. Still, I'd call that a Windows bug, not a git bug.
Not quite. On x86_32, for complicated and ultimately ridiculous but nevertheless valid reasons, lots of syscalls on musl use int $0x80. I have a patch to make this fixable but Linus shot it down. Maybe I should try again.
On x86_64, syscalls only use SYSCALL. It's very fast if audit and such are off and reasonably fast otherwise. (I extensively rewrote this code recently. Older teardowns of the syscall path are dated.)
