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Date: Thu, 11 Sep 2014 18:15:17 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Vincent Guittot <vincent.guittot@...aro.org> Cc: mingo@...nel.org, linux-kernel@...r.kernel.org, preeti@...ux.vnet.ibm.com, linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org, riel@...hat.com, Morten.Rasmussen@....com, efault@....de, nicolas.pitre@...aro.org, linaro-kernel@...ts.linaro.org, daniel.lezcano@...aro.org, dietmar.eggemann@....com Subject: Re: [PATCH v5 11/12] sched: replace capacity_factor by utilization On Tue, Aug 26, 2014 at 01:06:54PM +0200, Vincent Guittot wrote: > +static inline int group_has_free_capacity(struct sg_lb_stats *sgs, > + struct lb_env *env) > { > + if ((sgs->group_capacity_orig * 100) > > + (sgs->group_utilization * env->sd->imbalance_pct)) > + return 1; > + > + if (sgs->sum_nr_running < sgs->group_weight) > + return 1; > > + return 0; > +} > > +static inline int group_is_overloaded(struct sg_lb_stats *sgs, > + struct lb_env *env) > +{ > + if (sgs->sum_nr_running <= sgs->group_weight) > + return 0; > > + if ((sgs->group_capacity_orig * 100) < > + (sgs->group_utilization * env->sd->imbalance_pct)) > + return 1; > > + return 0; > } I'm confused about the utilization vs capacity_orig. I see how we should maybe scale things with the capacity when comparing between CPUs/groups, but not on the same CPU/group. I would have expected something simple like: static inline bool group_has_capacity() { /* Is there a spare cycle? */ if (sgs->group_utilization < sgs->group_weight * SCHED_LOAD_SCALE) return true; /* Are there less tasks than logical CPUs? */ if (sgs->sum_nr_running < sgs->group_weight) return true; return false; } Where group_utilization a pure sum of running_avg. Now this has a hole when there are RT tasks on the system, in that case the utilization will never hit 1, but we could fix that another way. I don't think the capacity_orig thing is right. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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