[Caml-list] troubling results from profiling: compare_val

[Caml-list] troubling results from profiling: compare_val

[David Monniaux]

Dear Caml developers,

I profiled some mixed C/Caml program and saw that it spends 11% of its
time in compare_val(), as well as an important total time in compare().

Our code uses some maps on strings and many comparisons on int64's.

On the one hand, I tend to think that invoking a function that begins by
examining the concrete types of the data structures it is passed to when
those types are known at compilation time is a bit inefficient. On the
other hand, maybe the slight overhead is drowned in the whole time
necessary to make a native call and do the necessary comparisons in the
native code.

Is there a way to get more precise information than the one supplied by
ocamlprof -p / gprof on Linux/x86? How about a library using the TSC? A
Caml interface to Papi?

Regards,

David Monniaux            http://www.di.ens.fr/~monniaux
Laboratoire d'informatique de l'École Normale Supérieure,
Paris, France

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RE: [Caml-list] troubling results from profiling: compare_val

[Mattias Waldau]

If you know that you have numbers, in many cases you can use
- (minus) as comparation operator. That speeds things up.

> Our code uses some maps on strings and many comparisons on int64's.
> 

/mattias

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RE: [Caml-list] troubling results from profiling: compare_val

[Alain.Frisch]

On Wed, 26 Feb 2003, Mattias Waldau wrote:

> If you know that you have numbers, in many cases you can use
> - (minus) as comparation operator. That speeds things up.

Beware of the modulo semantics of the arithmetic operator (-) !

# List.sort (fun x y -> x - y) [min_int;max_int];;
- : int list = [1073741823; -1073741824]

-- Alain
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