* Josh Poimboeuf <jpoim...@redhat.com> wrote:
> On Wed, Jun 08, 2016 at 09:56:12AM +0200, Ingo Molnar wrote:
> >
> > * Josh Poimboeuf <jpoim...@redhat.com> wrote:
> >
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -789,6 +789,13 @@ static void update_curr_fair(struct rq *rq)
> > > update_curr(cfs_rq_of(&rq->curr->se));
> > > }
> > >
> > > +void trace_sched_stat_register(void)
> > > +{
> > > +#ifdef CONFIG_SCHEDSTATS
> > > + force_schedstat_enabled();
> > > +#endif
> > > +}
> >
> > I think it would be cleaner to provide an empty force_schedstat_enabled()
> > definition in sched.h, on !CONFIG_SCHEDSTATS.
>
> Yes, agreed.
>
> > But it might make sense to further decouple schedstats from tracing?
>
> Looking at how we could do that:
>
> - The sched_stat_wait tracepoint is dependent on the wait_start schedstat.
Can we maintain wait_start unconditionally? Having config dependent tracepoints
sucks.
> - The sched_stat_sleep tracepoint is dependent on the sleep_start
> schedstat.
Ditto.
> - The sched_stat_iowait and sched_stat_blocked tracepoints are dependent
> on the block_start schedstat.
Ditto.
> We could move those three schedstats values out of sched_statistics and
> into sched_entity, and then always update them regardless of
> CONFIG_SCHEDSTATS.
>
> That would ensure these tracepoints always work. But then again it
> would add a little bit of runtime overhead.
>
> I don't have a strong opinion either way. Thoughts?
Please do a before/after 'size vmlinux' dump of a defconfig build with tracing
disabled. I.e. how much code overhead does the updating of those variables add?
Thanks,
Ingo
