static-keys

Static key is a mechanism used by Linux kernel to speed up checks of seldomly used features. We brought it to Rust userland applications!

Example

A common example is about some flags user passed from commandline options to a long-running CLI applications. It is annoying to check a value that will never be changed after application boot up:

let flag = CommandlineArgs::parse();
loop {
    if flag {
        do_something();
    }
    do_common_routines();
}

Although the if-check is just test-jnz instructions in x86, it can still be speedup. What about making the check just as a jmp (skip over the do_something branch) or nop (always do_something)? This is what static keys do. To put it simply, we modify the instruction at runtime. After getting the flag passed from commandline, we dynamically modify the if flag instruction to be a jmp or nop according to the flag value.

Usage

See Example.