Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 2 Aug 2018 18:07:49 +0200 | Subject | Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator |
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On Thu, 2 Aug 2018 at 18:00, Quentin Perret <quentin.perret@arm.com> wrote: > > 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@arm.com> 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@arm.com> 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 ?
So you have to wait for the next tick that will set the overutilized and disable the want_energy. Until this point, all new tasks will be put on the current cpu
> > Thanks, > Quentin
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