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XANMOD: fair: Remove all energy efficiency functions
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Signed-off-by: Alexandre Frade <kernel@xanmod.org>
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@xanmod
xanmod committed Jun 28, 2021
1 parent 6e7b703 commit 83d8887
Showing 1 changed file with 0 additions and 258 deletions.
258 changes: 0 additions & 258 deletions kernel/sched/fair.c
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Expand Up @@ -6569,256 +6569,6 @@ static unsigned long cpu_util_without(int cpu, struct task_struct *p)
return min_t(unsigned long, util, capacity_orig_of(cpu));
}

/*
* Predicts what cpu_util(@cpu) would return if @p was migrated (and enqueued)
* to @dst_cpu.
*/
static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
{
struct cfs_rq *cfs_rq = &cpu_rq(cpu)->cfs;
unsigned long util_est, util = READ_ONCE(cfs_rq->avg.util_avg);

/*
* If @p migrates from @cpu to another, remove its contribution. Or,
* if @p migrates from another CPU to @cpu, add its contribution. In
* the other cases, @cpu is not impacted by the migration, so the
* util_avg should already be correct.
*/
if (task_cpu(p) == cpu && dst_cpu != cpu)
lsub_positive(&util, task_util(p));
else if (task_cpu(p) != cpu && dst_cpu == cpu)
util += task_util(p);

if (sched_feat(UTIL_EST)) {
util_est = READ_ONCE(cfs_rq->avg.util_est.enqueued);

/*
* During wake-up, the task isn't enqueued yet and doesn't
* appear in the cfs_rq->avg.util_est.enqueued of any rq,
* so just add it (if needed) to "simulate" what will be
* cpu_util() after the task has been enqueued.
*/
if (dst_cpu == cpu)
util_est += _task_util_est(p);

util = max(util, util_est);
}

return min(util, capacity_orig_of(cpu));
}

/*
* compute_energy(): Estimates the energy that @pd would consume if @p was
* migrated to @dst_cpu. compute_energy() predicts what will be the utilization
* landscape of @pd's CPUs after the task migration, and uses the Energy Model
* to compute what would be the energy if we decided to actually migrate that
* task.
*/
static long
compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
{
struct cpumask *pd_mask = perf_domain_span(pd);
unsigned long cpu_cap = arch_scale_cpu_capacity(cpumask_first(pd_mask));
unsigned long max_util = 0, sum_util = 0;
int cpu;

/*
* The capacity state of CPUs of the current rd can be driven by CPUs
* of another rd if they belong to the same pd. So, account for the
* utilization of these CPUs too by masking pd with cpu_online_mask
* instead of the rd span.
*
* 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) {
unsigned long util_freq = cpu_util_next(cpu, p, dst_cpu);
unsigned long cpu_util, util_running = util_freq;
struct task_struct *tsk = NULL;

/*
* When @p is placed on @cpu:
*
* util_running = max(cpu_util, cpu_util_est) +
* max(task_util, _task_util_est)
*
* while cpu_util_next is: max(cpu_util + task_util,
* cpu_util_est + _task_util_est)
*/
if (cpu == dst_cpu) {
tsk = p;
util_running =
cpu_util_next(cpu, p, -1) + task_util_est(p);
}

/*
* Busy time computation: utilization clamping is not
* required since the ratio (sum_util / cpu_capacity)
* is already enough to scale the EM reported power
* consumption at the (eventually clamped) cpu_capacity.
*/
sum_util += effective_cpu_util(cpu, util_running, cpu_cap,
ENERGY_UTIL, NULL);

/*
* Performance domain frequency: utilization clamping
* must be considered since it affects the selection
* of the performance domain frequency.
* NOTE: in case RT tasks are running, by default the
* FREQUENCY_UTIL's utilization can be max OPP.
*/
cpu_util = effective_cpu_util(cpu, util_freq, cpu_cap,
FREQUENCY_UTIL, tsk);
max_util = max(max_util, cpu_util);
}

return em_cpu_energy(pd->em_pd, max_util, sum_util);
}

/*
* find_energy_efficient_cpu(): Find most energy-efficient target CPU for the
* waking task. find_energy_efficient_cpu() looks for the CPU with maximum
* spare capacity in each performance domain and uses it as a potential
* candidate to execute the task. Then, it uses the Energy Model to figure
* out which of the CPU candidates is the most energy-efficient.
*
* The rationale for this heuristic is as follows. In a performance domain,
* all the most energy efficient CPU candidates (according to the Energy
* Model) are those for which we'll request a low frequency. When there are
* several CPUs for which the frequency request will be the same, we don't
* have enough data to break the tie between them, because the Energy Model
* only includes active power costs. With this model, if we assume that
* frequency requests follow utilization (e.g. using schedutil), the CPU with
* the maximum spare capacity in a performance domain is guaranteed to be among
* the best candidates of the performance domain.
*
* In practice, it could be preferable from an energy standpoint to pack
* small tasks on a CPU in order to let other CPUs go in deeper idle states,
* but that could also hurt our chances to go cluster idle, and we have no
* ways to tell with the current Energy Model if this is actually a good
* idea or not. So, find_energy_efficient_cpu() basically favors
* cluster-packing, and spreading inside a cluster. That should at least be
* a good thing for latency, and this is consistent with the idea that most
* of the energy savings of EAS come from the asymmetry of the system, and
* not so much from breaking the tie between identical CPUs. That's also the
* reason why EAS is enabled in the topology code only for systems where
* SD_ASYM_CPUCAPACITY is set.
*
* NOTE: Forkees are not accepted in the energy-aware wake-up path because
* they don't have any useful utilization data yet and it's not possible to
* forecast their impact on energy consumption. Consequently, they will be
* placed by find_idlest_cpu() on the least loaded CPU, which might turn out
* to be energy-inefficient in some use-cases. The alternative would be to
* bias new tasks towards specific types of CPUs first, or to try to infer
* their util_avg from the parent task, but those heuristics could hurt
* other use-cases too. So, until someone finds a better way to solve this,
* let's keep things simple by re-using the existing slow path.
*/
static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
{
unsigned long prev_delta = ULONG_MAX, best_delta = ULONG_MAX;
struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
unsigned long cpu_cap, util, base_energy = 0;
int cpu, best_energy_cpu = prev_cpu;
struct sched_domain *sd;
struct perf_domain *pd;

rcu_read_lock();
pd = rcu_dereference(rd->pd);
if (!pd || READ_ONCE(rd->overutilized))
goto fail;

/*
* Energy-aware wake-up happens on the lowest sched_domain starting
* from sd_asym_cpucapacity spanning over this_cpu and prev_cpu.
*/
sd = rcu_dereference(*this_cpu_ptr(&sd_asym_cpucapacity));
while (sd && !cpumask_test_cpu(prev_cpu, sched_domain_span(sd)))
sd = sd->parent;
if (!sd)
goto fail;

sync_entity_load_avg(&p->se);
if (!task_util_est(p))
goto unlock;

for (; pd; pd = pd->next) {
unsigned long cur_delta, spare_cap, max_spare_cap = 0;
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;

util = cpu_util_next(cpu, p, cpu);
cpu_cap = capacity_of(cpu);
spare_cap = cpu_cap;
lsub_positive(&spare_cap, util);

/*
* Skip CPUs that cannot satisfy the capacity request.
* IOW, placing the task there would make the CPU
* overutilized. Take uclamp into account to see how
* much capacity we can get out of the CPU; this is
* aligned with sched_cpu_util().
*/
util = uclamp_rq_util_with(cpu_rq(cpu), util, p);
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) {
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) {
cur_delta = compute_energy(p, max_spare_cap_cpu, pd);
cur_delta -= base_energy_pd;
if (cur_delta < best_delta) {
best_delta = cur_delta;
best_energy_cpu = max_spare_cap_cpu;
}
}
}
unlock:
rcu_read_unlock();

/*
* Pick the best CPU if prev_cpu cannot be used, or if it saves at
* least 6% of the energy used by prev_cpu.
*/
if (prev_delta == ULONG_MAX)
return best_energy_cpu;

if ((prev_delta - best_delta) > ((prev_delta + base_energy) >> 4))
return best_energy_cpu;

return prev_cpu;

fail:
rcu_read_unlock();

return -1;
}

/*
* select_task_rq_fair: Select target runqueue for the waking task in domains
* that have the relevant SD flag set. In practice, this is SD_BALANCE_WAKE,
Expand All @@ -6844,14 +6594,6 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)

if (wake_flags & WF_TTWU) {
record_wakee(p);

if (sched_energy_enabled()) {
new_cpu = find_energy_efficient_cpu(p, prev_cpu);
if (new_cpu >= 0)
return new_cpu;
new_cpu = prev_cpu;
}

want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, p->cpus_ptr);
}

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