Re: GC time

[Markus Mottl <mottl@miss.wu-wien.ac.at>]

> >It there a (simple) way for me to measure the GC time
> >spent on executing ocamlopt-generated native code or
> >ocaml bytecode?
> 
> Not yet.  We may include GC timers in a future release of O'Caml, but
> starting and stopping the timer takes almost as much time as the GC
> itself, so you'll take a performance hit and the accuracy of the
> timings will not be very good.

It is possible to do an exact (cycle level) analysis on Alpha-processors
under Digitial Unix. The tool "pixie" allows insertion of profiling code
into any kind of binary executable. The resulting information is extremely
detailed and also accurately counts cycles consumed by the OCaml-GC. So if
you have access to such a machine, profiling gets easy...

Here, for example, the first lines of output of such a run:

---------------------------------------------------------------------------
2297470 cycles (0.0077 seconds at 299.40 megahertz)

    cycles %cycles  cum %  seconds     cycles  bytes procedure (file)
                                        /call  /line

    380979   16.58  16.58   0.0013         62      ? oldify (<sm>)
    315953   13.75  30.33   0.0011         45      ? Stream_get_data_66 (<sm>)
    192558    8.38  38.72   0.0006     192558      ? proc_at_0x12004f080 (<sm>)
    152879    6.65  45.37   0.0005        454      ? lex_engine (<sm>)
    152832    6.65  52.02   0.0005        159      ? parse_engine (<sm>)
    111860    4.87  56.89   0.0004         47      ? alloc_shr (<sm>)
    106617    4.64  61.53   0.0004         36      ? modify (<sm>)
---------------------------------------------------------------------------

Regards,
Markus Mottl

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl