sched/fair: Remove capacity inversion detection

Remove the capacity inversion detection which is now handled by
util_fits_cpu() returning -1 when we need to continue to look for a
potential CPU with better performance.

This ends up almost reverting patches below except for some comments:
commit da07d2f9 ("sched/fair: Fixes for capacity inversion detection")
commit aa69c36f ("sched/fair: Consider capacity inversion in util_fits_cpu()")
commit 44c7b80b ("sched/fair: Detect capacity inversion")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230201143628.270912-3-vincent.guittot@linaro.org

kernel/sched/fair.c

@@ -4476,17 +4476,9 @@ static inline int util_fits_cpu(unsigned long util,
 	 *
 	 * For uclamp_max, we can tolerate a drop in performance level as the
 	 * goal is to cap the task. So it's okay if it's getting less.
-	 *
-	 * In case of capacity inversion we should honour the inverted capacity
-	 * for both uclamp_min and uclamp_max all the time.
 	 */
-	capacity_orig = cpu_in_capacity_inversion(cpu);
-	if (capacity_orig) {
-		capacity_orig_thermal = capacity_orig;
-	} else {
-		capacity_orig = capacity_orig_of(cpu);
-		capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
-	}
+	capacity_orig = capacity_orig_of(cpu);
+	capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
 
 	/*
 	 * We want to force a task to fit a cpu as implied by uclamp_max.
@@ -9027,82 +9019,16 @@ static unsigned long scale_rt_capacity(int cpu)
 
 static void update_cpu_capacity(struct sched_domain *sd, int cpu)
 {
-	unsigned long capacity_orig = arch_scale_cpu_capacity(cpu);
 	unsigned long capacity = scale_rt_capacity(cpu);
 	struct sched_group *sdg = sd->groups;
-	struct rq *rq = cpu_rq(cpu);
 
-	rq->cpu_capacity_orig = capacity_orig;
+	cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(cpu);
 
 	if (!capacity)
 		capacity = 1;
 
-	rq->cpu_capacity = capacity;
-
-	/*
-	 * Detect if the performance domain is in capacity inversion state.
-	 *
-	 * Capacity inversion happens when another perf domain with equal or
-	 * lower capacity_orig_of() ends up having higher capacity than this
-	 * domain after subtracting thermal pressure.
-	 *
-	 * We only take into account thermal pressure in this detection as it's
-	 * the only metric that actually results in *real* reduction of
-	 * capacity due to performance points (OPPs) being dropped/become
-	 * unreachable due to thermal throttling.
-	 *
-	 * We assume:
-	 *   * That all cpus in a perf domain have the same capacity_orig
-	 *     (same uArch).
-	 *   * Thermal pressure will impact all cpus in this perf domain
-	 *     equally.
-	 */
-	if (sched_energy_enabled()) {
-		unsigned long inv_cap = capacity_orig - thermal_load_avg(rq);
-		struct perf_domain *pd;
-
-		rcu_read_lock();
-
-		pd = rcu_dereference(rq->rd->pd);
-		rq->cpu_capacity_inverted = 0;
-
-		for (; pd; pd = pd->next) {
-			struct cpumask *pd_span = perf_domain_span(pd);
-			unsigned long pd_cap_orig, pd_cap;
-
-			/* We can't be inverted against our own pd */
-			if (cpumask_test_cpu(cpu_of(rq), pd_span))
-				continue;
-
-			cpu = cpumask_any(pd_span);
-			pd_cap_orig = arch_scale_cpu_capacity(cpu);
-
-			if (capacity_orig < pd_cap_orig)
-				continue;
-
-			/*
-			 * handle the case of multiple perf domains have the
-			 * same capacity_orig but one of them is under higher
-			 * thermal pressure. We record it as capacity
-			 * inversion.
-			 */
-			if (capacity_orig == pd_cap_orig) {
-				pd_cap = pd_cap_orig - thermal_load_avg(cpu_rq(cpu));
-
-				if (pd_cap > inv_cap) {
-					rq->cpu_capacity_inverted = inv_cap;
-					break;
-				}
-			} else if (pd_cap_orig > inv_cap) {
-				rq->cpu_capacity_inverted = inv_cap;
-				break;
-			}
-		}
-
-		rcu_read_unlock();
-	}
-
-	trace_sched_cpu_capacity_tp(rq);
+	cpu_rq(cpu)->cpu_capacity = capacity;
+	trace_sched_cpu_capacity_tp(cpu_rq(cpu));
 
 	sdg->sgc->capacity = capacity;
 	sdg->sgc->min_capacity = capacity;

kernel/sched/sched.h

@@ -1044,7 +1044,6 @@ struct rq {
 
 	unsigned long		cpu_capacity;
 	unsigned long		cpu_capacity_orig;
-	unsigned long		cpu_capacity_inverted;
 
 	struct balance_callback *balance_callback;
 
@@ -2899,24 +2898,6 @@ static inline unsigned long capacity_orig_of(int cpu)
 	return cpu_rq(cpu)->cpu_capacity_orig;
 }
 
-/*
- * Returns inverted capacity if the CPU is in capacity inversion state.
- * 0 otherwise.
- *
- * Capacity inversion detection only considers thermal impact where actual
- * performance points (OPPs) gets dropped.
- *
- * Capacity inversion state happens when another performance domain that has
- * equal or lower capacity_orig_of() becomes effectively larger than the perf
- * domain this CPU belongs to due to thermal pressure throttling it hard.
- *
- * See comment in update_cpu_capacity().
- */
-static inline unsigned long cpu_in_capacity_inversion(int cpu)
-{
-	return cpu_rq(cpu)->cpu_capacity_inverted;
-}
-
 /**
  * enum cpu_util_type - CPU utilization type
  * @FREQUENCY_UTIL:	Utilization used to select frequency