RFR (S): JEP-142: Reduce Cache Contention on Specified Fields

[Michael Barker]

>  -XX:FieldPaddingWidth=64:  3.55 +- 0.03 nsec/op
>  -XX:FieldPaddingWidth=128: 3.54 +- 0.03 nsec/op

Do you have adjacent cache line prefetching supported/enabled?  These
numbers suggest that padding to 2 cache lines doesn't provide a
significant speed up over a single cache line.  If there isn't a large
benefit to padding to 128 bytes, should be set as the default?