Messages in this thread | | | Date | Thu, 2 Aug 2018 15:54:26 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5 12/14] sched/fair: Select an energy-efficient CPU on task wake-up |
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On Tue, Jul 24, 2018 at 01:25:19PM +0100, Quentin Perret wrote: > @@ -6385,18 +6492,26 @@ static int > select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags) > { > struct sched_domain *tmp, *sd = NULL; > + struct freq_domain *fd; > int cpu = smp_processor_id(); > int new_cpu = prev_cpu; > - int want_affine = 0; > + int want_affine = 0, want_energy = 0; > int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING); > > + rcu_read_lock(); > if (sd_flag & SD_BALANCE_WAKE) { > record_wakee(p); > - want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) > - && cpumask_test_cpu(cpu, &p->cpus_allowed); > + fd = rd_freq_domain(cpu_rq(cpu)->rd); > + want_energy = fd && !READ_ONCE(cpu_rq(cpu)->rd->overutilized); > + want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) && > + cpumask_test_cpu(cpu, &p->cpus_allowed); > + } > + > + if (want_energy) { > + new_cpu = find_energy_efficient_cpu(p, prev_cpu, fd); > + goto unlock; > } >
And I suppose you rely on the compiler to optimize that for the static key inside rd_freq_domain()... Does it do a good job of that?
That is, would not something like:
rcu_read_lock(); if (sd_flag & SD_BALANCE_WAKE) { record_wakee(p);
if (static_branch_unlikely(&sched_energy_present)) { struct root_domain *rd = cpu_rq(cpu)->rd; struct freq_domain *fd = rd_freq_domain(rd);
if (fd && !READ_ONCE(rd->overutilized)) { new_cpu = find_energy_efficient_cpu(p, prev_cpu, fd); goto unlock; } }
/* ... */ }
Be far more clear ?
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