when to remount sysfs ?

Hi: As i know , when kernel is booting , sysfs is mounted at /sys before the real root fs is mounted . Then , after the real root fs is mounted , when does i need to remount sysfs at the new /sys location ? I know the devfs is remounted by do_mount ("none", "/dev", "devfs", 0, "") , so how is that for sysfs? Thanks!