I don't understand. If bcantrill's description of VDSOs (buried in this presentation: https://www.youtube.com/watch?v=TrfD3pC0VSs) is accurate, then they're just a way to make certain syscalls faster, when syscalls are already fast enough.
they aren't. some syscalls get hammered so much by user space code that any overhead is too much overhead. especially with gettimeofday/clock_gettime which are used for timestamping and measuring intervals. you don't want overhead on your timing code.
