Reduce the number of digits shown in UI

[carllerche]

It probably doesn't make much sense to include fractions in the numbers displayed in the UI.

ref: https://news.ycombinator.com/item?id=29596537

[hawkw]

I think we probably do want one or two fractional digits, at least for larger units like seconds, but definitely not 4 like we have currently.

[pnkfelix]

Can we just vary the fraction so that we aim for 3 significant figures total when the non-fractional part is less than 1000? (And when its >= 1000, then the fractional part should be hidden.)

Is that the wrong way to look at this?

[hawkw]

not directly related, but we probably also want to format durations over one or two minutes as minutes + seconds, rather than as a large number of seconds, which it looks like std::time::Duration's fmt::Debug implementation doesn't do. So, at some point, we're definitely going to end up writing our own duration formatter, and we can probably implement significant figures logic there as well?

[carllerche]

I think we probably do want one or two fractional digits, at least for larger units like seconds, but definitely not 4 like we have currently.

Depends... 5m20s maybe, but 3.245ms... probably not. I think 3ms would make more sense there.