Request for review: 6888526 Linux getCurrentThreadCpuTime is drastically slower than Windows

[Andrew Haley]

The evaluation says:

"As the submitter notes the functionality exists but is disabled by
default. The user can easily enable it by specifying
-XX:+UseLinuxPosixThreadCPUClocks

"The functionality was added for JDK 6 under CR 6200022 but there was
concern at the time about enabling it by default (those concerns are
not documented in 6200022).

"Perhaps it is time to enable this feature by default?"

I changed the default for this parameter to true.

I tested this change on an older Linux system that does not have the
high-speed thread clock interface (Red Hat Enterprise Linux AS release
4, kernel 2.6.9).  The test case still works, but slowly.

On a more recent system (Fedora 12, kernel 2.6.31) the test case is
much speeded up.

Is there any more testing that I should do?

Patch at http://cr.openjdk.java.net/~aph/6888526/

OK to push?

Andrew.