RFR: 8232594: Make the output of the JFR command duration more user friendly

[Erik Gahlin]

Hi Chihiro,

I don't think 1 day is a good representation of for example 27 hours.  
The precision is too low.  I also think numbers should be rounded up 
where applicable.

When a duration is short, it is often convenient to use ms (with some 
fractions) instead of microseconds. It makes it easier to compare 
values. This is especially true if you are looking at multiple values 
and want to compare them, for example GC pause time.

It is probably a good idea to first decide how values should be 
formatted before attempting an implementation.

Erik

> Hi,
>
> I tried to implement this to output an accurate time duration.
> Could you review this, please?
>
> Is a rounded duration better than an exact duration?
>
> JBS https://bugs.openjdk.java.net/browse/JDK-8232594
> webrev http://cr.openjdk.java.net/~cito/JDK-8232594/webrev.00/
>
> Regards,
> Chihiro