Mongo currently uses gettimeofday() for all posix interval metrics. As this function is not monotonic, we may see anomalies under certain conditions; e.g. VMM live migration, some SMP process migrations, system sleep/suspend/hibernate, NTP or system date changes, TSC-related kernel or VMM bugs, etc.
The FineClock class (src/mongo/db/stats/fine_clock.h) implements a monotonic clock source, however the code is currently Linux specific and unused. The goal here would be to make this class fully functional on all platforms and ensure performance is >= gettimeofday(). It may also be worth migrating the win32 code from boost::xtime to QueryPerformanceCounter() or similar as boost::xtime has been deprecated.