Messages in this thread | | | Date | Thu, 2 Aug 2018 16:30:37 +0100 | From | Quentin Perret <> | Subject | Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator |
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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 ...
Sorry if that wasn't clear
> Then, select_task_rq_fair is called for a new task but util_avg is > still 0 at that time in the current code so you will have consistent > util_avg of the new task before and after calling > find_energy_efficient_cpu
New tasks don't go in find_energy_efficient_cpu(), because, as you said, they have no consistent util_avg yet when select_task_rq_fair() is called for the first time.
Thanks, Quentin
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