RFR: Implement heuristics to switch between merged and separate update-refs phase

[Roman Kennke]

Am 08.05.2017 um 21:57 schrieb Aleksey Shipilev:
> On 05/08/2017 09:52 PM, Roman Kennke wrote:
>> Am 08.05.2017 um 18:23 schrieb Aleksey Shipilev:
>>> On 05/08/2017 05:12 PM, Roman Kennke wrote:
>>>> This also means that, at least when running with adaptive heuristics
>>>> (the default), the argument -XX:+/-ShenandoahUpdateRefsEarly is unused.
>>> Um. I wonder if there is an option to turn off UR unconditionally. Should we
>>> rewire that flag have three values: always-on, always-off, adaptive?
>> Like this ?
>>
>> http://cr.openjdk.java.net/~rkennke/merge-uprefs/webrev.02/
> *) Um. AdaptiveHeuristics() would still execute ShenandoahHeuristics(), right?
> Which will then print the warning message?
>
>  227   } else if (strcmp(ShenandoahUpdateRefsEarly, "adaptive") == 0) {
>  228     log_warning(gc)("-XX:ShenandoahUpdateRefsEarly=adaptive only useful
> with -XX:ShenandoahGCHeuristics=adaptive. Defaulting to 'true' instead.");
>  229     _update_refs_early = true;
Duh.

Ok, I moved it all into ShenandoahHeuristics constructor now. Life's too
short.

> *) Leftover:
>
>  588     tty->print_cr("last cycle gap: %f ms", last_cycle_gap);
>
> Otherwise seems fine.
Removed.

http://cr.openjdk.java.net/~rkennke/merge-uprefs/webrev.03/
<http://cr.openjdk.java.net/%7Erkennke/merge-uprefs/webrev.03/>

Ok now?

Roman