Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator

[Quentin Perret]

On Thursday 02 Aug 2018 at 17:55:24 (+0200), Vincent Guittot wrote:
> On Thu, 2 Aug 2018 at 17:30, Quentin Perret <quentin.perret@xxxxxxx> wrote:
> >
> > On Thursday 02 Aug 2018 at 17:14:15 (+0200), Vincent Guittot wrote:
> > > On Thu, 2 Aug 2018 at 16:14, Quentin Perret <quentin.perret@xxxxxxx> wrote:
> > > > Good point, setting the util_avg to 0 for new tasks should help
> > > > filtering out those tiny tasks too. And that would match with the idea
> > > > of letting tasks build their history before looking at their util_avg ...
> > > >
> > > > But there is one difference w.r.t frequency selection. The current code
> > > > won't mark the system overutilized, but will let sugov raise the
> > > > frequency when a new task is enqueued. So in case of a fork bomb, we
> > >
> > > If the initial value of util_avg is 0, we should not have any impact
> > > on the util_avg of the cfs rq on which the task is attached, isn't it
> > > ? so this should not impact both the over utilization state and the
> > > frequency selected by sugov or I'm missing something ?
> >
> > What I tried to say is that setting util_avg to 0 for new tasks will
> > prevent schedutil from raising the frequency in case of a fork bomb, and
> > I think that could be an issue. And I think this isn't an issue with the
> > patch as-is ...
> 
> ok. So you also want to deal with fork bomb
> Not sure that you don't have some problem with current proposal too
> because select_task_rq_fair will always return prev_cpu because
> util_avg and util_est are 0 at that time

But find_idlest_cpu() should select a CPU using load in case of a forkee
no ?

Thanks,
Quentin