Messages in this thread | | | Date | Thu, 4 Oct 2018 10:34:57 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v7 11/14] sched/fair: Introduce an energy estimation helper function |
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On Wed, Sep 12, 2018 at 10:13:06AM +0100, Quentin Perret wrote: > +static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu) > +{ > + struct cfs_rq *cfs_rq = &cpu_rq(cpu)->cfs; > + unsigned long util_est, util = READ_ONCE(cfs_rq->avg.util_avg); > + > + /* > + * If @p migrates from @cpu to another, remove its contribution. Or, > + * if @p migrates from another CPU to @cpu, add its contribution. In > + * the other cases, @cpu is not impacted by the migration, so the > + * util_avg should already be correct. > + */ > + if (task_cpu(p) == cpu && dst_cpu != cpu) > + util = max_t(long, util - task_util(p), 0);
That's not quite right; what you want to check for is underflow, but the above also results in 0 if util - task_util() > LONG_MAX without an underflow.
You could write: sub_positive(&util, task_util(p));
> + else if (task_cpu(p) != cpu && dst_cpu == cpu) > + util += task_util(p); > + > + if (sched_feat(UTIL_EST)) { > + util_est = READ_ONCE(cfs_rq->avg.util_est.enqueued); > + > + /* > + * During wake-up, the task isn't enqueued yet and doesn't > + * appear in the cfs_rq->avg.util_est.enqueued of any rq, > + * so just add it (if needed) to "simulate" what will be > + * cpu_util() after the task has been enqueued. > + */ > + if (dst_cpu == cpu) > + util_est += _task_util_est(p); > + > + util = max(util, util_est); > + } > + > + return min_t(unsigned long, util, capacity_orig_of(cpu));
AFAICT both @util and capacity_orig_of() have 'unsigned long' as type.
> +} > + > +/* > + * compute_energy(): Estimates the energy that would be consumed if @p was > + * migrated to @dst_cpu. compute_energy() predicts what will be the utilization > + * landscape of the * CPUs after the task migration, and uses the Energy Model > + * to compute what would be the energy if we decided to actually migrate that > + * task. > + */ > +static long compute_energy(struct task_struct *p, int dst_cpu, > + struct perf_domain *pd)
static long compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
> +{ > + long util, max_util, sum_util, energy = 0; > + int cpu; > + > + while (pd) { > + max_util = sum_util = 0; > + /* > + * The capacity state of CPUs of the current rd can be driven by > + * CPUs of another rd if they belong to the same performance > + * domain. So, account for the utilization of these CPUs too > + * by masking pd with cpu_online_mask instead of the rd span. > + * > + * If an entire performance domain is outside of the current rd, > + * it will not appear in its pd list and will not be accounted > + * by compute_energy(). > + */ > + for_each_cpu_and(cpu, perf_domain_span(pd), cpu_online_mask) { > + util = cpu_util_next(cpu, p, dst_cpu); > + util = schedutil_freq_util(cpu, util, ENERGY_UTIL); > + max_util = max(util, max_util); > + sum_util += util; > + } > + > + energy += em_pd_energy(pd->obj, max_util, sum_util); > + pd = pd->next; > + }
No real strong preference, but you could write that like:
for (; pd; pd = pd->next) { }
> + > + return energy; > +}
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