Re: Huge slowdown since 6.0

[David Carlton <carlton at kealia dot com>]

On Fri, 20 Feb 2004 00:09:06 -0500, Daniel Jacobowitz <drow@false.org> said:
> My testcase is in C.

> These are all conditionalized on language_cplus.

> How can they possibly be to blame?  Well, they are.  And reverting the
> change for enumerators definitely won't do any harm.  Take a look at
> this, read it two or three times if necessary - it took me about a
> dozen:

>> > -                          &objfile->static_psymbols,
>> > +                          cu_language == language_cplus
>> > +                          ? &objfile->static_psymbols
>> > +                          : &objfile->global_psymbols,

> If I swap "static" and "global", it reduces GDB startup time by roughly
> 40% for glibc with debug information, which contains a lot of C
> enumerators.  I assume that is what you meant to do in the first
> place?

Um, yeah.  Oops.  That would qualify as an obvious fix.

There's one other interesting point here - where exactly is the
slowdown coming from?  After all, we generate the same number of
searches, and lookup_symbol can potentially look at all the static
psymbols just like it could look at all the global psymbols.  Not only
that, but looking at the static psymbols is vastly slower than looking
at the global psymbols (for no good reason, as far as I know, but
that's a separate issue; lookup_partial_symbol has issues).

But I suppose the point is that looking at all the static psymbols is
only a very last resort in lookup_symbol, so (as long as the symbol
you're looking for actually exists) it wouldn't get called very often.

Or is there something else that I'm missing?

David Carlton
carlton@kealia.com