* Tom Lane:
> On Linux (RHEL6, 2.4GHz x86_64), I find that gettimeofday(),
> clock_gettime(CLOCK_MONOTONIC), and clock_gettime(CLOCK_REALTIME)
> all take about 40ns. Of course gettimeofday() only has 1us resolution,
> but the other two have perhaps 10ns resolution (I get no duplicate
> readings in a tight loop). Other documented clockids include
> CLOCK_REALTIME_COARSE: about 10ns to read, but only 1ms resolution
> CLOCK_MONOTONIC_COARSE: about 12ns to read, but only 1ms resolution
> CLOCK_MONOTONIC_RAW: full resolution but very slow, ~145ns to read
> So CLOCK_MONOTONIC seems to be the thing to use here. It won't buy
> us anything speed-wise but the extra resolution will be nice.
> However, we need to do more research to see if this holds true on
> other popular distros.
Isn't this very specific to kernel and glibc versions, depending on
things like CONFIG_HZ settings and what level of vDSO support has been
backported?