ANDROID: sched: Allow EAS without schedutil

This effectively reverts 531b5c9f5c ("sched/topology: Make Energy
Aware Scheduling depend on schedutil"), and updates the documentation
accordingly.

In the context of GKI 2.0, some partners need to use a custom cpufreq
govenor, but would like to keep EAS enabled.

Remove the hard dependency between them.

Bug: 157580690
Signed-off-by: Quentin Perret <qperret@google.com>
Change-Id: Ied1c5aba6b692e26776b3e2c050780a67cc5bae1

Documentation/scheduler/sched-energy.rst

@@ -405,7 +405,7 @@ Consequently, the only sane governor to use together with EAS is schedutil,
 because it is the only one providing some degree of consistency between
 frequency requests and energy predictions.
 
-Using EAS with any other governor than schedutil is not supported.
+Using EAS with any other governor than schedutil is not recommended.
 
 
 6.5 Scale-invariant utilization signals

drivers/cpufreq/cpufreq.c

@@ -2472,7 +2472,6 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
 		ret = cpufreq_start_governor(policy);
 		if (!ret) {
 			pr_debug("governor change\n");
-			sched_cpufreq_governor_change(policy, old_gov);
 			return 0;
 		}
 		cpufreq_exit_governor(policy);

include/linux/cpufreq.h

@@ -979,14 +979,6 @@ static inline bool policy_has_boost_freq(struct cpufreq_policy *policy)
 }
 #endif
 
-#if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)
-void sched_cpufreq_governor_change(struct cpufreq_policy *policy,
-			struct cpufreq_governor *old_gov);
-#else
-static inline void sched_cpufreq_governor_change(struct cpufreq_policy *policy,
-			struct cpufreq_governor *old_gov) { }
-#endif
-
 extern void arch_freq_prepare_all(void);
 extern unsigned int arch_freq_get_on_cpu(int cpu);
 

kernel/sched/cpufreq_schedutil.c

@@ -914,36 +914,3 @@ static int __init sugov_register(void)
 	return cpufreq_register_governor(&schedutil_gov);
 }
 core_initcall(sugov_register);
-
-#ifdef CONFIG_ENERGY_MODEL
-extern bool sched_energy_update;
-extern struct mutex sched_energy_mutex;
-
-static void rebuild_sd_workfn(struct work_struct *work)
-{
-	mutex_lock(&sched_energy_mutex);
-	sched_energy_update = true;
-	rebuild_sched_domains();
-	sched_energy_update = false;
-	mutex_unlock(&sched_energy_mutex);
-}
-static DECLARE_WORK(rebuild_sd_work, rebuild_sd_workfn);
-
-/*
- * EAS shouldn't be attempted without sugov, so rebuild the sched_domains
- * on governor changes to make sure the scheduler knows about it.
- */
-void sched_cpufreq_governor_change(struct cpufreq_policy *policy,
-				  struct cpufreq_governor *old_gov)
-{
-	if (old_gov == &schedutil_gov || policy->governor == &schedutil_gov) {
-		/*
-		 * When called from the cpufreq_register_driver() path, the
-		 * cpu_hotplug_lock is already held, so use a work item to
-		 * avoid nested locking in rebuild_sched_domains().
-		 */
-		schedule_work(&rebuild_sd_work);
-	}
-
-}
-#endif

kernel/sched/topology.c

@@ -319,7 +319,6 @@ static void sched_energy_set(bool has_eas)
  *    2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy.
  *    3. no SMT is detected.
  *    4. the EM complexity is low enough to keep scheduling overheads low;
- *    5. schedutil is driving the frequency of all CPUs of the rd;
  *
  * The complexity of the Energy Model is defined as:
  *
@@ -339,15 +338,12 @@ static void sched_energy_set(bool has_eas)
  */
 #define EM_MAX_COMPLEXITY 2048
 
-extern struct cpufreq_governor schedutil_gov;
 static bool build_perf_domains(const struct cpumask *cpu_map)
 {
 	int i, nr_pd = 0, nr_cs = 0, nr_cpus = cpumask_weight(cpu_map);
 	struct perf_domain *pd = NULL, *tmp;
 	int cpu = cpumask_first(cpu_map);
 	struct root_domain *rd = cpu_rq(cpu)->rd;
-	struct cpufreq_policy *policy;
-	struct cpufreq_governor *gov;
 
 	if (!sysctl_sched_energy_aware)
 		goto free;
@@ -373,19 +369,6 @@ static bool build_perf_domains(const struct cpumask *cpu_map)
 		if (find_pd(pd, i))
 			continue;
 
-		/* Do not attempt EAS if schedutil is not being used. */
-		policy = cpufreq_cpu_get(i);
-		if (!policy)
-			goto free;
-		gov = policy->governor;
-		cpufreq_cpu_put(policy);
-		if (gov != &schedutil_gov) {
-			if (rd->pd)
-				pr_warn("rd %*pbl: Disabling EAS, schedutil is mandatory\n",
-						cpumask_pr_args(cpu_map));
-			goto free;
-		}
-
 		/* Create the new pd and add it to the local list. */
 		tmp = pd_init(i);
 		if (!tmp)