Commit 9b340131 authored by Dietmar Eggemann's avatar Dietmar Eggemann Committed by Peter Zijlstra
Browse files

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: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Tested-by: default avatarLukasz Luba <lukasz.luba@arm.com>
Link: https://lkml.kernel.org/r/20220621090414.433602-6-vdonnefort@google.com
parent ec4fc801

kernel/sched/fair.c

+13 −9
Original line number Diff line number Diff line
@@ -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;