gettimeofday() resolution in Linux?

Hi,

I would like to ask a few questions about how Linux keeps time.

As far as I understand,
1. Linux's time resolution is 10ms, as defined by HZ=100.
2. gettimeofday() can get time in microseconds, but I'm not sure about
the accuracy of the time finer than 10ms. Sometimes gettimeofday( )
can even give me microseconds results rolled backwards in time, which
I suspect could be caused by its accuracy. My question here is "how
accurate is the time from gettimeofday()"
3. If I want to increase the time resolution to 1ms, I can possibly
change HZ=1000, but if I want 1usec resolution, how can I do that? It
would be too busy for the processor to handle so frequent timer
interrupts if I just increase HZ=1000000.

Many thanks/muchas gracias/Danke vielmals!