sched/fair: Use the same cpumask per-PD throughout find_energy_efficient_cpu()

The Perf Domain (PD) cpumask (struct em_perf_domain.cpus) stays
invariant after Energy Model creation, i.e. it is not updated after
CPU hotplug operations.

That's why the PD mask is used in conjunction with the cpu_online_mask
(or Sched Domain cpumask). Thereby the cpu_online_mask is fetched
multiple times (in compute_energy()) during a run-queue selection
for a task.

cpu_online_mask may change during this time which can lead to wrong
energy calculations.

To be able to avoid this, use the select_rq_mask per-cpu cpumask to
create a cpumask out of PD cpumask and cpu_online_mask and pass it
through the function calls of the EAS run-queue selection path.

The PD cpumask for max_spare_cap_cpu/compute_prev_delta selection
(find_energy_efficient_cpu()) is now ANDed not only with the SD mask
but also with the cpu_online_mask. This is fine since this cpumask
has to be in syc with the one used for energy computation
(compute_energy()).
An exclusive cpuset setup with at least one asymmetric CPU capacity
island (hence the additional AND with the SD cpumask) is the obvious
exception here.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lkml.kernel.org/r/20220621090414.433602-6-vdonnefort@google.com

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e3f750135f78a4fcdda7d30f306296ce43aa650d..46d669297b1f069a7777e830d9268da72dee152a 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6709,14 +6709,14 @@ static unsigned long cpu_util_without(int cpu, struct task_struct *p)
  * task.
  */
 static long
-compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
+compute_energy(struct task_struct *p, int dst_cpu, struct cpumask *cpus,
+              struct perf_domain *pd)
 {
-       struct cpumask *pd_mask = perf_domain_span(pd);
        unsigned long max_util = 0, sum_util = 0, cpu_cap;
        int cpu;
 
-       cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
-       cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
+       cpu_cap = arch_scale_cpu_capacity(cpumask_first(cpus));
+       cpu_cap -= arch_scale_thermal_pressure(cpumask_first(cpus));
 
        /*
         * The capacity state of CPUs of the current rd can be driven by CPUs
@@ -6727,7 +6727,7 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
         * If an entire pd is outside of the current rd, it will not appear in
         * its pd list and will not be accounted by compute_energy().
         */
-       for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
+       for_each_cpu(cpu, cpus) {
                unsigned long util_freq = cpu_util_next(cpu, p, dst_cpu);
                unsigned long cpu_util, util_running = util_freq;
                struct task_struct *tsk = NULL;
@@ -6814,6 +6814,7 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
  */
 static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 {
+       struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
        unsigned long prev_delta = ULONG_MAX, best_delta = ULONG_MAX;
        struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
        int cpu, best_energy_cpu = prev_cpu, target = -1;
@@ -6848,7 +6849,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
                unsigned long base_energy_pd;
                int max_spare_cap_cpu = -1;
 
-               for_each_cpu_and(cpu, perf_domain_span(pd), sched_domain_span(sd)) {
+               cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
+
+               for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
                        if (!cpumask_test_cpu(cpu, p->cpus_ptr))
                                continue;
 
@@ -6885,12 +6888,12 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
                        continue;
 
                /* Compute the 'base' energy of the pd, without @p */
-               base_energy_pd = compute_energy(p, -1, pd);
+               base_energy_pd = compute_energy(p, -1, cpus, 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 = compute_energy(p, prev_cpu, cpus, pd);
                        if (prev_delta < base_energy_pd)
                                goto unlock;
                        prev_delta -= base_energy_pd;
@@ -6899,7 +6902,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 
                /* 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 = compute_energy(p, max_spare_cap_cpu, cpus,
+                                                  pd);
                        if (cur_delta < base_energy_pd)
                                goto unlock;
                        cur_delta -= base_energy_pd;