It's up the the individual collector to decide what to report. I'm not sure how the young collector in marksweep (called `PS Scavenge`) returns collection time.

Here is an example of code that treats collectors differently, but they just do young vs old (whereas we probably want concurrent vs not).
http://svn.cometd.org/trunk/cometd-java/cometd-java-client/src/test/java/org/cometd/client/StatisticsHelper.java