[PATCH 13/15] sched/cputime: Consolidate get_cpu_[idle|iowait]_time_us()
From: Frederic Weisbecker <frederic@kernel.org>
Date: 2026-01-16 14:53:55
Also in:
linux-pm, linux-s390, lkml
Subsystem:
cpu frequency scaling framework, nohz, dynticks support, scheduler, the rest · Maintainers:
"Rafael J. Wysocki", Viresh Kumar, Anna-Maria Behnsen, Frederic Weisbecker, Ingo Molnar, Thomas Gleixner, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds
get_cpu_idle/iowait_time_us() may ultimately fail if generic vtime accounting is enabled. The ad-hoc replacement solution by cpufreq is to compute jiffies minus the whole busy cputime. Although the intention should provide a coherent low resolution estimation of the idle and iowait time, the implementation is buggy because jiffies don't start at 0. Enhance instead get_cpu_[idle|iowait]_time_us() to provide support for vtime generic accounting. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> --- drivers/cpufreq/cpufreq.c | 29 +---------------------------- include/linux/kernel_stat.h | 3 +++ include/linux/tick.h | 4 ---- kernel/sched/cputime.c | 14 ++++++++++---- 4 files changed, 14 insertions(+), 36 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 4472bb1ec83c..ecb9634cd06b 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c@@ -130,38 +130,11 @@ struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy) } EXPORT_SYMBOL_GPL(get_governor_parent_kobj); -static inline u64 get_cpu_idle_time_jiffy(unsigned int cpu, u64 *wall) -{ - struct kernel_cpustat kcpustat; - u64 cur_wall_time; - u64 idle_time; - u64 busy_time; - - cur_wall_time = jiffies64_to_nsecs(get_jiffies_64()); - - kcpustat_cpu_fetch(&kcpustat, cpu); - - busy_time = kcpustat.cpustat[CPUTIME_USER]; - busy_time += kcpustat.cpustat[CPUTIME_SYSTEM]; - busy_time += kcpustat.cpustat[CPUTIME_IRQ]; - busy_time += kcpustat.cpustat[CPUTIME_SOFTIRQ]; - busy_time += kcpustat.cpustat[CPUTIME_STEAL]; - busy_time += kcpustat.cpustat[CPUTIME_NICE]; - - idle_time = cur_wall_time - busy_time; - if (wall) - *wall = div_u64(cur_wall_time, NSEC_PER_USEC); - - return div_u64(idle_time, NSEC_PER_USEC); -} - u64 get_cpu_idle_time(unsigned int cpu, u64 *wall, int io_busy) { u64 idle_time = get_cpu_idle_time_us(cpu, io_busy ? wall : NULL); - if (idle_time == -1ULL) - return get_cpu_idle_time_jiffy(cpu, wall); - else if (!io_busy) + if (!io_busy) idle_time += get_cpu_iowait_time_us(cpu, wall); return idle_time;
diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index e1efd26e56f0..e59916477075 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h@@ -133,6 +133,9 @@ static inline bool kcpustat_idle_dyntick(void) } #endif /* CONFIG_NO_HZ_COMMON */ +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); + /* Fetch cputime values when vtime is disabled on a CPU */ static inline u64 kcpustat_field_default(enum cpu_usage_stat usage, int cpu) {
diff --git a/include/linux/tick.h b/include/linux/tick.h
index ac76ae9fa36d..1296cba67bee 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h@@ -138,8 +138,6 @@ extern bool tick_nohz_idle_got_tick(void); extern ktime_t tick_nohz_get_next_hrtimer(void); extern ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next); extern unsigned long tick_nohz_get_idle_calls_cpu(int cpu); -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 int tick_nohz_tick_stopped(void) { return 0; }
@@ -160,8 +158,6 @@ static inline ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next) *delta_next = TICK_NSEC; return *delta_next; } -static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; } -static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } #endif /* !CONFIG_NO_HZ_COMMON */ /*
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 9906abe5d7bc..f0620b429698 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c@@ -511,6 +511,13 @@ u64 kcpustat_field_iowait(int cpu) nr_iowait_cpu(cpu), ktime_get()); } EXPORT_SYMBOL_GPL(kcpustat_field_iowait); +#else +static u64 kcpustat_field_dyntick(int cpu, enum cpu_usage_stat idx, + bool compute_delta, ktime_t now) +{ + return kcpustat_cpu(cpu).cpustat[idx]; +} +#endif /* CONFIG_NO_HZ_COMMON */ static u64 get_cpu_sleep_time_us(int cpu, enum cpu_usage_stat idx, bool compute_delta, u64 *last_update_time)
@@ -519,7 +526,7 @@ static u64 get_cpu_sleep_time_us(int cpu, enum cpu_usage_stat idx, u64 res; if (vtime_generic_enabled_cpu(cpu)) - return -1; + res = kcpustat_field(idx, cpu); else res = kcpustat_field_dyntick(cpu, idx, compute_delta, now);
@@ -544,7 +551,7 @@ static u64 get_cpu_sleep_time_us(int cpu, enum cpu_usage_stat idx, * This time is measured via accounting rather than sampling, * and is as accurate as ktime_get() is. * - * Return: -1 if generic vtime is enabled, else total idle time of the @cpu + * Return: total idle time of the @cpu */ u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) {
@@ -568,7 +575,7 @@ EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); * This time is measured via accounting rather than sampling, * and is as accurate as ktime_get() is. * - * Return: -1 if generic vtime is enabled, else total iowait time of @cpu + * Return: total iowait time of @cpu */ u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) {
@@ -576,7 +583,6 @@ u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) nr_iowait_cpu(cpu), last_update_time); } EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); -#endif /* CONFIG_NO_HZ_COMMON */ /* * Use precise platform statistics if available:
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2.51.1