Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 15 Mar 2023 16:32:27 +0100 | Subject | Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated |
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On Wed, 15 Mar 2023 at 14:36, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 15/03/2023 11:21, Vincent Guittot wrote: > > On Wed, 15 Mar 2023 at 11:15, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > >> > >> On 15/03/2023 09:42, Vincent Guittot wrote: > >>> On Wed, 15 Mar 2023 at 08:18, Vincent Guittot > >>> <vincent.guittot@linaro.org> wrote: > >>>> > >>>> On Tue, 14 Mar 2023 at 18:16, Peter Zijlstra <peterz@infradead.org> wrote: > >>>>> > >>>>> On Tue, Mar 14, 2023 at 02:24:37PM +0100, Vincent Guittot wrote: > >>>>> > > [...] > > >> Isn't there an issue with this approach on asymmetric CPU capacity systems? > >> > >> We do a sync_entity_load_avg() in select_task_rq_fair() > >> (find_energy_efficient_cpu() for EAS and select_idle_sibling() for CAS) > >> to sync cfs_rq and se. > > > > ah yes, I forgot this point. > > That being said, is it a valid problem for EAS based system ? I mean > > we are trying to fix a vruntime comparison overflow that can happen > > with a very long sleeping task (around 200 days) while only a very low > > weight entity is always running during those 200 days. > > True. Definitively very unlikely. But it's not only EAS, any asymmetric > CPU capacity wakeup wouldn't have this check in this case. > > This dependency between sync_entity_load_avg() and the overflow > detection would be very hard to spot though (in case > sync_entity_load_avg() would get introduced in more common wakeup paths > later).
fair enough
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