Messages in this thread | | | Date | Tue, 19 Jun 2018 10:36:01 +0530 | From | Pavan Kondeti <> | Subject | Re: [RFC PATCH v3 09/10] sched/fair: Select an energy-efficient CPU on task wake-up |
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On Mon, May 21, 2018 at 03:25:04PM +0100, Quentin Perret wrote:
<snip>
> + if (cpumask_test_cpu(prev_cpu, &p->cpus_allowed)) > + prev_energy = best_energy = compute_energy(p, prev_cpu); > + else > + prev_energy = best_energy = ULONG_MAX; > + > + for_each_freq_domain(sfd) { > + unsigned long spare_cap, max_spare_cap = 0; > + int max_spare_cap_cpu = -1; > + unsigned long util; > + > + /* Find the CPU with the max spare cap in the freq. dom. */ > + for_each_cpu_and(cpu, freq_domain_span(sfd), sched_domain_span(sd)) { > + if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) > + continue; > + > + if (cpu == prev_cpu) > + continue; > + > + /* Skip CPUs that will be overutilized */ > + util = cpu_util_wake(cpu, p) + task_util; > + cpu_cap = capacity_of(cpu); > + if (cpu_cap * 1024 < util * capacity_margin) > + continue; > + > + spare_cap = cpu_cap - util; > + if (spare_cap > max_spare_cap) { > + max_spare_cap = spare_cap; > + max_spare_cap_cpu = cpu; > + } > + } > + > + /* Evaluate the energy impact of using this CPU. */ > + if (max_spare_cap_cpu >= 0) { > + cur_energy = compute_energy(p, max_spare_cap_cpu); > + if (cur_energy < best_energy) { > + best_energy = cur_energy; > + best_energy_cpu = max_spare_cap_cpu; > + } > + } > + } > + > + /* > + * We pick the best CPU only if it saves at least 1.5% of the > + * energy used by prev_cpu. > + */ > + if ((prev_energy - best_energy) > (prev_energy >> 6)) > + return best_energy_cpu; > + > + return prev_cpu; > +}
We are comparing the best_energy_cpu against prev_cpu even when prev_cpu can't accommodate the waking task. Is this intentional? Should not we discard the prev_cpu if it can't accommodate the task.
This can potentially make a BIG task run on a lower capacity CPU until load balancer kicks in and corrects the situation.
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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