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Re: [GOOGLE] Increase max-early-inliner-iterations to 2 for profile-gen and use


> On Sat, Oct 18, 2014 at 3:27 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
> >> The difference in instrumentation runtime is huge -- as topn profiler
> >> is pretty expensive to run.
> >>
> >> With FDO, it is probably better to make early inlining more aggressive
> >> in order to get more context sensitive profiling.
> >
> > I agree with that, I just would like to understand where increasing the iterations
> > helps and if we can handle it without iterating (because Richi originally requested to
> > drop the iteration for correcness issues)
> > Do you have some examples?
> 
> We can do FDO experiment by shutting down einline. (Note that
> increasing iteration to 2 did not actually improve performance with
> our benchmarks).

I would be more interested in case where increasing iteration to 2 actually
improves train run perfomrance. (einline was originally invented to make
profiling useable on tramp3d ;)
It seems to me that the cases handled by iteration are rather rare, so I am
suprised you get important benefit from these. Perhaps we miss something
obvious here.

Honza
> 
> David
> 
> > Honza
> >>
> >> David
> >>
> >> On Sat, Oct 18, 2014 at 10:05 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
> >> >> Increasing the number of early inliner iterations from 1 to 2 enables more
> >> >> indirect calls to be promoted/inlined before instrumentation. This in turn
> >> >> reduces the instrumentation overhead, particularly for more expensive indirect
> >> >> call topn profiling.
> >> >
> >> > How much difference you get here? One posibility would be also to run specialized
> >> > ipa-cp before profile instrumentation.
> >> >
> >> > Honza
> >> >>
> >> >> Passes internal testing and regression tests. Ok for google/4_9?
> >> >>
> >> >> 2014-10-18  Teresa Johnson  <tejohnson@google.com>
> >> >>
> >> >>         Google ref b/17934523
> >> >>         * opts.c (finish_options): Increase max-early-inliner-iterations to 2
> >> >>         for profile-gen and profile-use builds.
> >> >>
> >> >> Index: opts.c
> >> >> ===================================================================
> >> >> --- opts.c      (revision 216286)
> >> >> +++ opts.c      (working copy)
> >> >> @@ -870,6 +869,14 @@ finish_options (struct gcc_options *opts, struct g
> >> >>          opts->x_param_values, opts_set->x_param_values);
> >> >>      }
> >> >>
> >> >> +  if (opts->x_profile_arc_flag
> >> >> +      || opts->x_flag_branch_probabilities)
> >> >> +    {
> >> >> +      maybe_set_param_value
> >> >> +       (PARAM_EARLY_INLINER_MAX_ITERATIONS, 2,
> >> >> +        opts->x_param_values, opts_set->x_param_values);
> >> >> +    }
> >> >> +
> >> >>    if (!(opts->x_flag_auto_profile
> >> >>          || (opts->x_profile_arc_flag || opts->x_flag_branch_probabilities)))
> >> >>      {
> >> >>
> >> >>
> >> >> --
> >> >> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413


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