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Date: -- (:)
From: Damien Bobillot <damien.bobillot@m...>
Subject: Re: [Caml-list] Profiling garbage

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Jon Harrop wrote :

> I've recently been trying to optimize Presenta. The profiling results
> surprised me. Most of the time was spent in the GC, invoked by
> "<spontaneous>". I assumed this meant that the GC was recycling =20
> enormous
> amounts of garbage from the old generation. Had it been recycled =20
> from the
> young generation then I assume the calls to the (minor) GC would be =20=

> invoked
> by the allocating function - is that right?
>
> Anyway, the best way I found to track down the offending function =20
> was to write
> lots of extra code to spew out Gc.stat results and look at the =20
> amount of data
> being allocated by each function call. Doing this by hand is very =20
> tedious, of
> course. So I'm wondering, are there any tools to profile allocation =20=

> and
> collection on a per function basis for OCaml code? I'm thinking of =20
> something
> along the lines of gprof results but showing space rather than time =20=

> taken.
>
> I managed to find the offending function by hand this time - it was
> retypesetting the entire document every frame, regenerating the =20
> scene graph.
> Memoizing it improved the performance of the whole program by an =20
> order of
> magnitude. So this is definitely an optimisation trick worth =20
> remembering...

You may use GC den-bugging information by adding the following =20
commands at the beginning of your code :
     Gc.set { (Gc.get()) with Gc.verbose =3D 1+2+4+8 };;

This will print a message on stdout every time a minor or major =20
collection is done, and some other actions like heap growing.

You may print at any time the current GC statistics (number of =20
collections, current heap size, total number of allocated bytes=85) with =
:
     Gc.print_stat stderr;;

It's also possible to tune the GC parameter to reduce frequency of =20
minor collections (by increasing the minor heap size for instance) =20
and some other things.

For more information, have a look at :
http://caml.inria.fr/pub/docs/manual-ocaml/libref/Gc.html

--=20
Damien alias Schmurtz
aim:goim?screenname=3Dschmuuurtz


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