Re: [Texmacs-dev] Speedup in startup time

[Gubinelli Massimiliano]

Hi,


On 12 juin 09, at 14:51, Norbert Nemec wrote:

> Hi there,
>
> I just tried to do some profiling of TeXmacs and managed to produce  
> a small but significant speedup in the startup time: from 2.0 sec to  
> 1.8 sec (averaged over several runs of "time texmacs -q").
>
> Turns out that quite some time was spent in frequent calls to the  
> routine implemented as
>
> -------
> inline bool is_none (url u) { return u->t == tuple ("none"); }
> -------
>
> replacing this by a comparison with a global variable initialized  
> just once. Attached is a tiny patch that implements this change.
>
> Far more important than this change itself, however, is the general  
> question that it poses: how many more objects are there in the code  
> that are initialized from a constant string over and over again? How  
> much efficiency could we gain from a global symbol table that is  
> initialized just once?

I've noticed that in TeXmacs code sometimes constant strings are used  
as atoms ( or symbols ) without having a special handling and thus a  
bit inefficiently as you also noticed. It would be nice to do the  
following experiment: implement a symbol hashset where you register  
common strings. A new constructor for symbol strings is then added  
which checks if the string is already present in the hashset and  
eventually returns this instance. Then string comparison can be  
implemented as a two steps procedure: 1) pointer comparison and when  
this fails 2) actual string comparison. This would add a small  
overhead over the plain string comparison but maybe with added  
benefits to be quantified by experimentation (since I have no idea  
about the quantity of code which uses strings as atoms).

best,
max

> Greetings,
> Norbert
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