Re: [RFC PATCH 09/13] sched/fair: core wide vruntime comparison

Vineeth Remanan Pillai
2020-04-15T21:25:13Z

> > > You forgot the time complexity analysis.
> >
> > This is a mistake and the adjust should be needed only once when core
> > scheduling is initially enabled. It is an initialization thing and there
> > is no reason to do it in every invocation of coresched_adjust_vruntime().
>
> Correction...
> I meant there is no need to call coresched_adjust_vruntime() in every
> invocation of update_core_cfs_rq_min_vruntime().

Due to the checks in place, update_core_cfs_rq_min_vruntime should
not be calling coresched_adjust_vruntime more than once between a
coresched enable/disable. Once the min_vruntime is adjusted, we depend
only on rq->core and the other sibling's min_vruntime will not grow
until coresched disable.

I did some micro benchmark tests today to verify this and observed
that coresched_adjust_vruntime called at most once between a coresched
enable/disable.

Thanks,
Vineeth