On Sat, Oct 18, 2014 at 4:26 PM, Jan Hubicka <hubi...@ucw.cz> wrote:
>> On Sat, Oct 18, 2014 at 3:27 PM, Jan Hubicka <hubi...@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 ;)
What is special about tram3d ?
> 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.
For training run performance, as in this case, einline helps reducing
indirect calls thus reduces instrumentation overhead. Instrumentation
has another side-effect that it changes function body size, thus can
reduce the amount of ipa-inline later.
David
>
> Honza
>>
>> David
>>
>> > Honza
>> >>
>> >> David
>> >>
>> >> On Sat, Oct 18, 2014 at 10:05 AM, Jan Hubicka <hubi...@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 <tejohn...@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 | tejohn...@google.com |
>> >> >> 408-460-2413
