RFR: Reinstate reference processing shortcut, missing after merge

[Zhengyu Gu]

Looks good.

-Zhengyu

On 06/06/2018 09:32 AM, Aleksey Shipilev wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/refproc-shortcut-reinstate/webrev.01/
> 
> This was accidentally removed during recent merges to sh/jdk. This shortcut is still effective,
> because upstream work to mitigate these latencies had not yet landed in the mainline.
> 
> For example, Serial:
> 
> Without patch:
> 
>   Pause Final Mark (N) = 0.15 s (a = 1709 us) (n =    89)
>     Finish Queues      = 0.01 s (a =  164 us) (n =    89)
>     Weak References    = 0.12 s (a = 1386 us) (n =    89)
>       Process          = 0.12 s (a = 1381 us) (n =    89)
>     Prepare Evacuation = 0.01 s (a =  139 us) (n =    89)
> 
> With patch:
> 
>   Pause Final Mark (N) = 0.03 s (a =  334 us) (n =    95)
>     Finish Queues      = 0.01 s (a =  103 us) (n =    95)
>     Weak References    = 0.01 s (a =   83 us) (n =    95)  // <--- !!!
>       Process          = 0.01 s (a =   79 us) (n =    95)
>     Prepare Evacuation = 0.01 s (a =  130 us) (n =    95)
> 
> Testing: hotspot_gc_shenandoah, some benchmarks
> 
> Thanks,
> -Aleksey
>