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Date: Thu, 30 Jun 2016 08:49:58 +0100 From: Morten Rasmussen <morten.rasmussen@....com> To: Sai Gurrappadi <sgurrappadi@...dia.com> Cc: peterz@...radead.org, mingo@...hat.com, dietmar.eggemann@....com, yuyang.du@...el.com, vincent.guittot@...aro.org, mgalbraith@...e.de, linux-kernel@...r.kernel.org, Peter Boonstoppel <pboonstoppel@...dia.com> Subject: Re: [PATCH v2 11/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups On Thu, Jun 23, 2016 at 02:20:48PM -0700, Sai Gurrappadi wrote: > Hi Morten, > > On 06/22/2016 10:03 AM, Morten Rasmussen wrote: > > [...] > > > > > +/* > > + * group_smaller_cpu_capacity: Returns true if sched_group sg has smaller > > + * per-cpu capacity than sched_group ref. > > + */ > > +static inline bool > > +group_smaller_cpu_capacity(struct sched_group *sg, struct sched_group *ref) > > +{ > > + return sg->sgc->max_capacity * capacity_margin < > > + ref->sgc->max_capacity * 1024; > > +} > > + > > static inline enum > > group_type group_classify(struct sched_group *group, > > struct sg_lb_stats *sgs) > > @@ -6892,6 +6903,19 @@ static bool update_sd_pick_busiest(struct lb_env *env, > > if (sgs->avg_load <= busiest->avg_load) > > return false; > > > > + if (!(env->sd->flags & SD_ASYM_CPUCAPACITY)) > > + goto asym_packing; > > + > > + /* Candidate sg has no more than one task per cpu and has > > + * higher per-cpu capacity. Migrating tasks to less capable > > + * cpus may harm throughput. Maximize throughput, > > + * power/energy consequences are not considered. > > + */ > > + if (sgs->sum_nr_running <= sgs->group_weight && > > + group_smaller_cpu_capacity(sds->local, sg)) > > + return false; > > + > > +asym_packing: > > What about the case where IRQ/RT work reduces the capacity of some of > these bigger CPUs? sgc->max_capacity might not necessarily capture > that case. Right, we could possibly improve this by using min_capacity instead, but we could end up allowing tasks to be pulled to lower capacity cpus just because one big cpu has reduced capacity due to RT/IRQ pressure and therefore has lowered the groups min_capacity. Ideally we should check all the capacities, but that complicates things a lot. Would you prefer min_capacity instead, or attempts to consider all the cpu capacities available in both groups?
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