[xdebug-general] Mysterious "cycle 2" entry in profile

I am seeing some confusing and possibly inaccurate profiling results
with xdebug 2.0.0 and PHP 5.2.3. My phpinfo() output is attached. The
program being profiled is a custom branch of MediaWiki, which can be
found at: http://svn.wikimedia.org/viewvc/mediawiki/branches/
liquidthreads

In kcachegrind, a 'function' called <cycle 2> (including the
brackets) is shown as taking 99% of the total execution time. This is
distinct from from the "cycle 2" annotation which appears on other
functions. The <cycle 2> 'function' appears to be called from many
places throughout the program, and to invoke other functions.

I suspect that <cycle 2> may be some kind of allocation or garbage
collection routine, but couldn't find anything about it with google.
Memory usage does not go significantly up or down near the places
where it appears to be invoked from.

Since the profiling output is large, I will refrain from attaching it
unless asked.

Any help figuring out what this is would be very helpful.

Thanks!

--
David McCabe