Re: gdb script performance

[Daniel Jacobowitz <drow@false.org>]

On Thu, Oct 05, 2006 at 05:29:30PM +0200, Jean-Marc Saffroy wrote:
> On Thu, 5 Oct 2006, Daniel Jacobowitz wrote:
> 
> >If you would like to see if further improvement is possible, you should
> >build a GDB with profiling enabled (--enable-profiling at configure
> >time), and use the maint set profile command to get a profile; then
> >post exact data from it.
> 
> Please find attached gprof output (this is with gdb 6.5 + 
> gdb-lookup-internal-first-3.patch running the lsmaps script I posted 
> earlier).
> 
> Thanks for helping!

 26.14    381.31   381.31   141867     2.69     3.50  find_pc_sect_psymtab
 18.54    651.82   270.51   331876     0.82     0.82  find_pc_sect_section
 17.88    912.69   260.87 144847060     0.00     0.00  lookup_partial_symbol
 11.01   1073.33   160.64 1254595136     0.00     0.00  strcmp_iw
  4.98   1145.97    72.64    34010     2.14    16.50  lookup_symbol_aux_psymtabs
  4.78   1215.73    69.75     9584     7.28     8.12  fixup_section
  4.46   1280.79    65.06                             lbasename
  3.42   1330.64    49.85    12183     4.09     4.09  lookup_partial_symtab
  1.83   1357.34    26.70 33844664     0.00     0.00  strcmp_iw_ordered
  1.68   1381.82    24.48 1288426966     0.00     0.00  symbol_natural_name
  1.09   1397.71    15.89 1288426966     0.00     0.00  symbol_search_name

Well then.  Observations:
  - We're looking up partial symbols way too often.
  - It's taking way too long.
  - And oh my lord is that a lot of calls to the (fairly inefficient)
    strcmp_iw.

It looks like only about three calls to find_pc_sect_psymtab per
expression evaluation, which is bad but not too bad - sounds like
a last-searched-item cache may be useful.

(To be clear: I don't have time to work on this just now.)

-- 
Daniel Jacobowitz
CodeSourcery