cpufreq: ondemand: Simplify idle cputime granularity test

cpufreq calls get_cpu_idle_time_us() just to know if idle cputime
accounting has a nanoseconds granularity.

Use the appropriate indicator instead to make that deduction.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://patch.msgid.link/aXozx0PXutnm8ECX@localhost.localdomain
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: Frederic Weisbecker

drivers/cpufreq/cpufreq_ondemand.c

@@ -334,17 +334,12 @@ static void od_free(struct policy_dbs_info *policy_dbs)
 static int od_init(struct dbs_data *dbs_data)
 {
 	struct od_dbs_tuners *tuners;
-	u64 idle_time;
-	int cpu;
 
 	tuners = kzalloc(sizeof(*tuners), GFP_KERNEL);
 	if (!tuners)
 		return -ENOMEM;
 
-	cpu = get_cpu();
-	idle_time = get_cpu_idle_time_us(cpu, NULL);
-	put_cpu();
-	if (idle_time != -1ULL) {
+	if (tick_nohz_is_active()) {
 		/* Idle micro accounting is supported. Use finer thresholds */
 		dbs_data->up_threshold = MICRO_FREQUENCY_UP_THRESHOLD;
 	} else {

include/linux/tick.h

@@ -126,6 +126,7 @@ enum tick_dep_bits {
 
 #ifdef CONFIG_NO_HZ_COMMON
 extern bool tick_nohz_enabled;
+extern bool tick_nohz_is_active(void);
 extern bool tick_nohz_tick_stopped(void);
 extern bool tick_nohz_tick_stopped_cpu(int cpu);
 extern void tick_nohz_idle_stop_tick(void);
@@ -142,6 +143,7 @@ extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
 extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
 #else /* !CONFIG_NO_HZ_COMMON */
 #define tick_nohz_enabled (0)
+static inline bool tick_nohz_is_active(void) { return false; }
 static inline int tick_nohz_tick_stopped(void) { return 0; }
 static inline int tick_nohz_tick_stopped_cpu(int cpu) { return 0; }
 static inline void tick_nohz_idle_stop_tick(void) { }

kernel/time/hrtimer.c

@@ -943,7 +943,7 @@ void clock_was_set(unsigned int bases)
 	cpumask_var_t mask;
 	int cpu;
 
-	if (!hrtimer_hres_active(cpu_base) && !tick_nohz_active)
+	if (!hrtimer_hres_active(cpu_base) && !tick_nohz_is_active())
 		goto out_timerfd;
 
 	if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {

kernel/time/tick-internal.h

@@ -156,7 +156,6 @@ static inline void tick_nohz_init(void) { }
 #endif
 
 #ifdef CONFIG_NO_HZ_COMMON
-extern unsigned long tick_nohz_active;
 extern void timers_update_nohz(void);
 extern u64 get_jiffies_update(unsigned long *basej);
 # ifdef CONFIG_SMP
@@ -171,7 +170,6 @@ extern void timer_expire_remote(unsigned int cpu);
 # endif
 #else /* CONFIG_NO_HZ_COMMON */
 static inline void timers_update_nohz(void) { }
-#define tick_nohz_active (0)
 #endif
 
 DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);

kernel/time/tick-sched.c

@@ -693,7 +693,7 @@ void __init tick_nohz_init(void)
  * NO HZ enabled ?
  */
 bool tick_nohz_enabled __read_mostly  = true;
-unsigned long tick_nohz_active  __read_mostly;
+static unsigned long tick_nohz_active  __read_mostly;
 /*
  * Enable / Disable tickless mode
  */
@@ -704,6 +704,12 @@ static int __init setup_tick_nohz(char *str)
 
 __setup("nohz=", setup_tick_nohz);
 
+bool tick_nohz_is_active(void)
+{
+	return tick_nohz_active;
+}
+EXPORT_SYMBOL_GPL(tick_nohz_is_active);
+
 bool tick_nohz_tick_stopped(void)
 {
 	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

kernel/time/timer.c

@@ -281,7 +281,7 @@ DEFINE_STATIC_KEY_FALSE(timers_migration_enabled);
 
 static void timers_update_migration(void)
 {
-	if (sysctl_timer_migration && tick_nohz_active)
+	if (sysctl_timer_migration && tick_nohz_is_active())
 		static_branch_enable(&timers_migration_enabled);
 	else
 		static_branch_disable(&timers_migration_enabled);