RFR (S): Percentile levels in -Xlog:gc+stats

[Aleksey Shipilev]

On 01/09/2017 11:48 AM, Roman Kennke wrote:
> Maybe instead of multiplying by 1000, measure more precisely?

We are measuring precisely: the counters reply in floating-point seconds, so
multiplying to 1K or 1M gives you integral milliseconds and microseconds,
respectively. HDR storage would coarsen, though, to get footprint advantages.

> Can't we have both max/SD and percentile stats? Or does it not make
> sense at all to see max/sd?

SD is useless for non-normal distributions. Well, average is misleading too,
unless levels say the distribution looks uniform/normal enough. The last level
was supposed to be maximum, but it might be not evident from the logging.
Changed it to explicit "max":

  Concurrent Marking Times   =    15.24 s (avg =    64594 us)
    (num =   236, lvls (10% step, us) =
       273, 463, 609, 863, 1055, 1895, 185547, 199219, 199219, max = 204852)

Is this better? Ok to push?

Thanks,
-Aleksey