Re: Hunting for performance regressions in libstdc++

[Paolo Carlini <pcarlini at suse dot de>]

Dan Kegel wrote:

> I have a sneaking suspicion that some of my app's
> performance problems might be due to gcc-3.4.3's libstdc++
> being somehow slower than SGI's STL, so I'm planning
> on doing some performance testing of various implementations
> of STL.
>
> Rather than building my app with the various STLs
> (which might be somewhat painful), I'd like to start
> with small to medium benchmarks.

[...]

I'm sorry, Dan, but frankly I'm finding quite a few inexact and even
misleading points in your message. In sparse order:

First, the "STL" delivered in gcc-3.4.x is *very* similar to the
original SGI STL, which constitutes our traditional code base: I would
be *very* surprised to see important performance regressions due to
those very minor bug fixes. Maybe you are mistaking the whole C++
runtime for the "STL"?

All the benchmarks that you mentioned make *very* little or no use of
the C++ library.

Besides a few problems in very specific areas (see Bugzilla, of course)
we are not aware of performance regressions wrt v2 (quite to the
contrary!). Don't you believe that a good amount of profiling of your
application is in order before chasing, generically, "performance
regressions in libstdc++"? I don't see it mentioned and, in general,
it's definitely the first thing to do and the way we took care ourselves
of problems in the past.

Thanks,
Paolo.