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

[Xinliang David Li <davidxl at google dot com>]

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).

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