This bug is a followup of JDK-8160350 - cannot truss jdk9 [ solaris ]. During investigation of that bug it became clear that the implementation, behaviour and usage of os::elapsedVTime() and the associated functions os::supports_vtime(), os::enable_vtime() and os::vtime_enabled() are inconsistent between platforms.

The issues are:

* Calls to os::elapsedVTime() are not being guarded in some places by a call to os::supports_vtime(), e.g. G1CMTask::do_marking_step() / G1CMTask::regular_clock_call()

* When thread CPU time is unavailable on a particular platform (e.g. BSD), total process CPU time is used instead, so on BSD the GC marking tasks may expire much earlier than on other platforms.

* If the underlying system call to get vtime fails, platforms may either return 0 or fall back to returning total process CPU time. That means that delta calculations based on sucessive values returned by os::elapsedVTime() could give bizarre results.

This area needs looking at carefully and decisions making about what the required cross-platform behaviour should be before the code is cleaned up.

See also the discussion at http://mail.openjdk.java.net/pipermail/hotspot-dev/2016-July/023784.html