RFR(XXS) 8217785: Padding ParallelTaskTerminator::_offerred_termination variable

[zgu at redhat.com]

Hi,

Could I have reviews for this small enhancement, that pads
_offer_termination variable into a separate cacheline? cause the
variable may be highly contended during task termination.

Bug: https://bugs.openjdk.java.net/browse/JDK-8217785
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8217785/webrev.00/

Test:
  hotspot_gc (+/- UseOWSTTaskTerminator) on Linux x64 (fastdebug and
release)


Thanks,

-Zhengyu