Re: tuning ld performance

[Michael Matz <matz at suse dot de>]

Hi,

On Mon, 26 Jan 2004, Andy Chittenden wrote:

> Secondly, after putting in the return statement, the next routine on the
> radar, bfd_hash_lookup, is taking 67% of CPU. As the major callers are
> _bfd_stringtab_add (from _bfd_link_section_stabs) and
> _bfd_link_section_stabs itself, it seems this could be stabs related but we
> obviously need them for debugging.

This is probably related to section merging of string tabs (although for 
stabs I'm not sure).

> Again, is there an easy way of either making this routine more efficient
> or removing calls to it?

There is no totally easy way.  One way I tried is to make GCC emit the 
hash value for each string and use that one while merging (instead of 
calculating it on demand).  But the major time sink in that routine 
actually are cache misses, and those don't go away, because while merging 
the strings they still have to be compared (i.e. read in).  That said the 
resulting ld was a bit faster, but not that much.  And at the expense of 
larger debug sections because of the added hash value per string.


Ciao,
Michael.