First plans on a profiler

[Daniel Kraft]

Hi all,

here are some first thoughts on implementing the profiler; so far I've 
not yet tried to actually hack together something based on them, but 
welcome any comments!  (As you of course know the internal working of 
Octave by far better than I do.)

At first, I would like to experiment with exact profiling on the level 
of functions.  For this, I would like to measure the time spent in each 
individual function -- possibly by doing something like (just as kind of 
"pseudo-code" of course):

function bar ()
  time = 0;
  start = cputime ();

  ... some code ...

  end = cputime ();
  time = time + (end - start);
  bar ();
  start = cputime ();

  ... some more code ...

  end = cputime ();
  time = time + (end - start);
end

And keeping track of "own" time for each function this way.  We'll see 
then by experiment whether this gives acceptable performance and whether 
the resolution of the timer is well enough to make this feasible.

Note that we probably even have to do the timing with unwind_protect (or 
rather some equivalent handling directly in the interpreter of course) 
in order to ensure correct working even in the presence of errors thrown.

I tried a quick search of the octave's pt-* code but wasn't able to find 
where function calls are made or which structures represent functions 
defined in .m files.  (I found fct-handle, but am not sure whether this 
is actually really involved when calling any function or only for stuff 
like anonymous functions or doing foo = @bar?)

Do you think we should store timing information directly in the function 
object in the syntax tree?  I thought so first, but then it came to my 
mind that with that, it would possibly be harder to iterate over all 
functions called during the last profiling session to get the output 
together and clear the times when necessary...  So an alternative would 
be to have a seperate "profiler" class store all the data in some kind 
of map which includes all functions as keys (either hashed on the 
function name or the pointer to the function object).  What do you think 
there?

I'm really looking forward to trying my luck on this! :)  Yours,
Daniel

PS: I won't have access to my mails over the weekend, but can come back 
to your replies on Sunday evening or Monday.

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