RFR(S) 8205921: Optimizing best-of-2 work stealing queue selection

[Zhengyu Gu]

Hi,

Please review this small enhancement base on paper [1], that keeps the 
last successfully stolen queue as one of best-of-2 candidates for work 
stealing.

Based on experiments done by Thomas Schatzl and myself, it shows 
positive impacts on task termination and average pause time.


Bug: https://bugs.openjdk.java.net/browse/JDK-8205921
Webrev: http://cr.openjdk.java.net/~zgu/8205921/webrev.00/index.html


Test:
   hotspot_gc on Linux 64 (fastdebug and release)


[1] Characterizing and Optimizing Hotspot Parallel Garbage
     Collection on Multicore Systems
     http://ranger.uta.edu/~jrao/papers/EuroSys18.pdf

Thanks,

-Zhengyu