wait_event()\ wait_event_interruptible()\ wait_event_interruptible_timeout() and wake_up()

Hi All, Let us assume that multiple processes are waiting on wait_event()\ wait_event_interruptible()\ wait_event_interruptible_timeout(), which process gets woken up on calling wake_up()?? I presume wake_up() picks one process, but is there any algorithm to pick which process? -- Thanks, Sekhar