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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
This commit is contained in:
Pierre Gondois 2021-05-04 10:07:42 +01:00 committed by Peter Zijlstra
parent e5e678e4fe
commit 8d4c97c105
1 changed files with 24 additions and 17 deletions
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41
kernel/sched/fair.c
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@ -6687,13 +6687,10 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
for (; pd; pd = pd->next) {
unsigned long cur_delta, spare_cap, max_spare_cap = 0;
bool compute_prev_delta = false;
unsigned long base_energy_pd;
int max_spare_cap_cpu = -1;
/* Compute the 'base' energy of the pd, without @p */
base_energy_pd = compute_energy(p, -1, pd);
base_energy += base_energy_pd;
for_each_cpu_and(cpu, perf_domain_span(pd), sched_domain_span(sd)) {
if (!cpumask_test_cpu(cpu, p->cpus_ptr))
continue;
@ -6714,25 +6711,35 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
if (!fits_capacity(util, cpu_cap))
continue;
/* Always use prev_cpu as a candidate. */
if (cpu == prev_cpu) {
prev_delta = compute_energy(p, prev_cpu, pd);
prev_delta -= base_energy_pd;
best_delta = min(best_delta, prev_delta);
}
/*
* Find the CPU with the maximum spare capacity in
* the performance domain
*/
if (spare_cap > max_spare_cap) {
/* Always use prev_cpu as a candidate. */
compute_prev_delta = true;
} else if (spare_cap > max_spare_cap) {
/*
* Find the CPU with the maximum spare capacity
* in the performance domain.
*/
max_spare_cap = spare_cap;
max_spare_cap_cpu = cpu;
}
}
/* Evaluate the energy impact of using this CPU. */
if (max_spare_cap_cpu >= 0 && max_spare_cap_cpu != prev_cpu) {
if (max_spare_cap_cpu < 0 && !compute_prev_delta)
continue;
/* Compute the 'base' energy of the pd, without @p */
base_energy_pd = compute_energy(p, -1, pd);
base_energy += base_energy_pd;
/* Evaluate the energy impact of using prev_cpu. */
if (compute_prev_delta) {
prev_delta = compute_energy(p, prev_cpu, pd);
prev_delta -= base_energy_pd;
best_delta = min(best_delta, prev_delta);
}
/* Evaluate the energy impact of using max_spare_cap_cpu. */
if (max_spare_cap_cpu >= 0) {
cur_delta = compute_energy(p, max_spare_cap_cpu, pd);
cur_delta -= base_energy_pd;
if (cur_delta < best_delta) {