Use jiffies and not do_gettimeofday() for latency tracking

jiffies are gauranteed to be monotonically increasing, and also
take less overhead in run-time, and about resolution - they are
good enough for the check against 10ms IO latency.
Remove some superfluous symbol exports

Symbols with names such as these should not be exported, they don't
match the module from which they originate and therefore clutter
the global symbol namespace. Should re-think about how to re-export
them later, if needed.