Re: Tooltips GC overhead

[Stefan Monnier <monnier@iro.umontreal.ca>]

> Just looking at the implementation of Fcons, I find it hard to believe
> a single comparison can have any significant effect on its efficiency.
> So I'm unsure how this could be of any practical concern.

Fcons is a core operation executed fairly frequently, so any slowdown
(no matter how small) needs to be justified by a major advantage.

Making the allocation profiler (which so far has never been useful to
anyone, AFAICT) slightly more precise, is not obviously a "major
advantage".  At the very least, I'd need positive proof that the extra
precision has been useful at least once.

>> > In any case, it's much better than the current useless profile.
>> I'm not convinced it'd make it sufficiently better
> Well, it allowed me in this case to identify the source of the problem
> quickly, efficiently, and accurately.

IIUC, something *else* allowed you to do that.  I don't think anyone
has actually tried to improve the precision of the allocation profiler
and found it to help in this case.
It's quite possible that some other problems might still prevent it from
being useful in this case.

>> I'd be OK with adding this "more precise allocation profiler" as
>> a compile-time option, so we could at least see if the improved
>> precision does make it more useful.
> IME, compile-time options of this kind are rarely useful, because they
> are never there when you need them.  Especially if the person who
> needs to perform measurements doesn't build their Emacs.

Until I have positive proof that the extra precision is useful in some
cases, I'll reject such changes in the default build.  So it's either
"rejected" or "depends on a compile-time option" for now.


        Stefan