RFR: Take boost mode into account when calculating duration of gc

[Erik Österlund]

Hi Per,

One step in the right direction. Looks good.

Thanks,
/Erik

On 2018-03-05 15:24, Per Liden wrote:
> When using boost mode (i.e. when we're using all available worker 
> threads instead of ConcGCThreads) we typically complete a GC cycle 
> much faster than normal (as intended). However, this causes the 
> "duration of gc" calculations to be artificially deflated, can later 
> lead to a situation where we risk starting a GC cycle too late. This 
> patch corrects the "duration of gc" calculation by taking the "boost 
> factor" into account.
>
> http://cr.openjdk.java.net/~pliden/zgc/normalized_duration/webrev.0/
>
> /Per