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Message-ID: <20260116145208.87445-14-frederic@kernel.org>
Date: Fri, 16 Jan 2026 15:52:06 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
"Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Anna-Maria Behnsen <anna-maria@...utronix.de>,
Ben Segall <bsegall@...gle.com>,
Boqun Feng <boqun.feng@...il.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Heiko Carstens <hca@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>,
Jan Kiszka <jan.kiszka@...mens.com>,
Joel Fernandes <joelagnelf@...dia.com>,
Juri Lelli <juri.lelli@...hat.com>,
Kieran Bingham <kbingham@...nel.org>,
Madhavan Srinivasan <maddy@...ux.ibm.com>,
Mel Gorman <mgorman@...e.de>,
Michael Ellerman <mpe@...erman.id.au>,
Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
Nicholas Piggin <npiggin@...il.com>,
"Paul E . McKenney" <paulmck@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Sven Schnelle <svens@...ux.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Uladzislau Rezki <urezki@...il.com>,
Valentin Schneider <vschneid@...hat.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Xin Zhao <jackzxcui1989@....com>,
linux-pm@...r.kernel.org,
linux-s390@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 13/15] sched/cputime: Consolidate get_cpu_[idle|iowait]_time_us()
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@...nel.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:
--
2.51.1
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