sched/fair: Only compute base_energy_pd if necessary
find_energy_efficient_cpu() searches the best energy CPU to place a task on. To do so, the energy of each performance domain (pd) is computed w/ and w/o the task placed on it. The energy of a pd w/o the task (base_energy_pd) is computed prior knowing whether a CPU is available in the pd. Move the base_energy_pd computation after looping through the CPUs of a pd and only compute it if at least one CPU is available. Suggested-by: Xuewen Yan <xuewen.yan@unisoc.com> Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Lukasz Luba <lukasz.luba@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Reviewed-by: Vincent Donnefort <vincent.donnefort@arm.com> Link: https://lkml.kernel.org/r/20210504090743.9688-2-Pierre.Gondois@arm.com
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@ -6687,13 +6687,10 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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for (; pd; pd = pd->next) {
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unsigned long cur_delta, spare_cap, max_spare_cap = 0;
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bool compute_prev_delta = false;
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unsigned long base_energy_pd;
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int max_spare_cap_cpu = -1;
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/* Compute the 'base' energy of the pd, without @p */
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base_energy_pd = compute_energy(p, -1, pd);
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base_energy += base_energy_pd;
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for_each_cpu_and(cpu, perf_domain_span(pd), sched_domain_span(sd)) {
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if (!cpumask_test_cpu(cpu, p->cpus_ptr))
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continue;
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@ -6714,25 +6711,35 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
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if (!fits_capacity(util, cpu_cap))
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continue;
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/* Always use prev_cpu as a candidate. */
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if (cpu == prev_cpu) {
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prev_delta = compute_energy(p, prev_cpu, pd);
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prev_delta -= base_energy_pd;
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best_delta = min(best_delta, prev_delta);
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}
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/*
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* Find the CPU with the maximum spare capacity in
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* the performance domain
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*/
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if (spare_cap > max_spare_cap) {
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/* Always use prev_cpu as a candidate. */
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compute_prev_delta = true;
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} else if (spare_cap > max_spare_cap) {
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/*
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* Find the CPU with the maximum spare capacity
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* in the performance domain.
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*/
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max_spare_cap = spare_cap;
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max_spare_cap_cpu = cpu;
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}
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}
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/* Evaluate the energy impact of using this CPU. */
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if (max_spare_cap_cpu >= 0 && max_spare_cap_cpu != prev_cpu) {
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if (max_spare_cap_cpu < 0 && !compute_prev_delta)
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continue;
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/* Compute the 'base' energy of the pd, without @p */
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base_energy_pd = compute_energy(p, -1, pd);
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base_energy += base_energy_pd;
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/* Evaluate the energy impact of using prev_cpu. */
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if (compute_prev_delta) {
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prev_delta = compute_energy(p, prev_cpu, pd);
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prev_delta -= base_energy_pd;
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best_delta = min(best_delta, prev_delta);
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}
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/* Evaluate the energy impact of using max_spare_cap_cpu. */
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if (max_spare_cap_cpu >= 0) {
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cur_delta = compute_energy(p, max_spare_cap_cpu, pd);
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cur_delta -= base_energy_pd;
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if (cur_delta < best_delta) {
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