Messages in this thread |  | | From | Pavan Kondeti <> | Date | Tue, 29 Aug 2017 10:15:58 +0530 | Subject | Re: [RFC 2/3] sched/fair: use util_est in LB |
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On Fri, Aug 25, 2017 at 3:50 PM, Patrick Bellasi <patrick.bellasi@arm.com> wrote: > When the scheduler looks at the CPU utlization, the current PELT value > for a CPU is returned straight away. In certain scenarios this can have > undesired side effects on task placement. >
<snip>
> +/** > + * cpu_util_est: estimated utilization for the specified CPU > + * @cpu: the CPU to get the estimated utilization for > + * > + * The estimated utilization of a CPU is defined to be the maximum between its > + * PELT's utilization and the sum of the estimated utilization of the tasks > + * currently RUNNABLE on that CPU. > + * > + * This allows to properly represent the expected utilization of a CPU which > + * has just got a big task running since a long sleep period. At the same time > + * however it preserves the benefits of the "blocked load" in describing the > + * potential for other tasks waking up on the same CPU. > + * > + * Return: the estimated utlization for the specified CPU > + */ > +static inline unsigned long cpu_util_est(int cpu) > +{ > + struct sched_avg *sa = &cpu_rq(cpu)->cfs.avg; > + unsigned long util = cpu_util(cpu); > + > + if (!sched_feat(UTIL_EST)) > + return util; > + > + return max(util, util_est(sa, UTIL_EST_LAST)); > +} > + > static inline int task_util(struct task_struct *p) > { > return p->se.avg.util_avg; > @@ -6007,11 +6033,19 @@ static int cpu_util_wake(int cpu, struct task_struct *p) > > /* Task has no contribution or is new */ > if (cpu != task_cpu(p) || !p->se.avg.last_update_time) > - return cpu_util(cpu); > + return cpu_util_est(cpu); > > capacity = capacity_orig_of(cpu); > util = max_t(long, cpu_rq(cpu)->cfs.avg.util_avg - task_util(p), 0); > > + /* > + * Estimated utilization tracks only tasks already enqueued, but still > + * sometimes can return a bigger value than PELT, for example when the > + * blocked load is negligible wrt the estimated utilization of the > + * already enqueued tasks. > + */ > + util = max_t(long, util, cpu_util_est(cpu)); > +
We are supposed to discount the task's util from its CPU. But the cpu_util_est() can potentially return cpu_util() which includes the task's utilization.
Thanks, Pavan
-- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
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