profiling a self compile

[Henry Cejtin]

The  <unknown> times (13.72% of 522.19 CPU seconds, or 71.64 seconds) is time
spent in the shared libraries.  This either means time actually spent  there,
or  time  spent in the system as a result of a system call (with the C system
call in the shared library).  Was your system time actually this large?  This
strikes me as pretty huge.  Also a lot of time in GC-related areas.  How high
was the percentage of time spent in the GC?

Is it my imagination, or is it true that with the current native back end and
profiler the output of mlprof seems harder to trace back to source code?