path: root/Revert-XANMOD-fair-Remove-all-energy-efficiency-functions.patch

From fb398de362e0dd83013990ceebe79d9b4e2438bd Mon Sep 17 00:00:00 2001
From: Scott B <arglebargle@arglebargle.dev>
Date: Thu, 10 Feb 2022 05:48:41 -0800
Subject: [PATCH] Revert "XANMOD: fair: Remove all energy efficiency functions"

This reverts commit 05bdfcdb4122ff03c18c3f3e9ba5c59684484ef8.
---
 kernel/sched/fair.c | 273 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 273 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b9f607aeee97..069e01772d92 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6609,6 +6609,271 @@ 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;
+	unsigned long _cpu_cap = cpu_cap;
+	int cpu;
+
+	_cpu_cap -= arch_scale_thermal_pressure(cpumask_first(pd_mask));
+
+	/*
+	 * 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.
+		 */
+		cpu_util = effective_cpu_util(cpu, util_running, cpu_cap,
+					      ENERGY_UTIL, NULL);
+
+		sum_util += min(cpu_util, _cpu_cap);
+
+		/*
+		 * 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, min(cpu_util, _cpu_cap));
+	}
+
+	return em_cpu_energy(pd->em_pd, max_util, sum_util, _cpu_cap);
+}
+
+/*
+ * 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;
+	int cpu, best_energy_cpu = prev_cpu, target = -1;
+	unsigned long cpu_cap, util, base_energy = 0;
+	struct sched_domain *sd;
+	struct perf_domain *pd;
+
+	rcu_read_lock();
+	pd = rcu_dereference(rd->pd);
+	if (!pd || READ_ONCE(rd->overutilized))
+		goto unlock;
+
+	/*
+	 * 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 unlock;
+
+	target = prev_cpu;
+
+	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;
+		bool compute_prev_delta = false;
+		unsigned long base_energy_pd;
+		int max_spare_cap_cpu = -1;
+
+		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;
+
+			if (cpu == prev_cpu) {
+				/* 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;
+			}
+		}
+
+		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);
+			if (prev_delta < base_energy_pd)
+				goto unlock;
+			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);
+			if (cur_delta < base_energy_pd)
+				goto unlock;
+			cur_delta -= base_energy_pd;
+			if (cur_delta < best_delta) {
+				best_delta = cur_delta;
+				best_energy_cpu = max_spare_cap_cpu;
+			}
+		}
+	}
+	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) ||
+	    (prev_delta - best_delta) > ((prev_delta + base_energy) >> 4))
+		target = best_energy_cpu;
+
+	return target;
+
+unlock:
+	rcu_read_unlock();
+
+	return target;
+}
+
 /*
  * 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,
@@ -6636,6 +6901,14 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 	lockdep_assert_held(&p->pi_lock);
 	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);
 	}
 
-- 
2.35.1