From: Josh Don <joshdon@xxxxxxxxxx>
[ Upstream commit a130e8fbc7de796eb6e680724d87f4737a26d0ac ]
/proc/uptime reports idle time by reading the CPUTIME_IDLE field from
the per-cpu kcpustats. However, on NO_HZ systems, idle time is not
continually updated on idle cpus, leading this value to appear
incorrectly small.
/proc/stat performs an accounting update when reading idle time; we
can use the same approach for uptime.
With this patch, /proc/stat and /proc/uptime now agree on idle time.
Additionally, the following shows idle time tick up consistently on an
idle machine:
(while true; do cat /proc/uptime; sleep 1; done) | awk '{print $2-prev; prev=$2}'
Reported-by: Luigi Rizzo <lrizzo@xxxxxxxxxx>
Signed-off-by: Josh Don <joshdon@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210827165438.3280779-1-joshdon@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/proc/stat.c | 4 ++--
fs/proc/uptime.c | 14 +++++++++-----
include/linux/kernel_stat.h | 1 +
3 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 4695b6de31512..3bed48d8228b4 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -23,7 +23,7 @@
#ifdef arch_idle_time
-static u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
+u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
{
u64 idle;
@@ -45,7 +45,7 @@ static u64 get_iowait_time(struct kernel_cpustat *kcs, int cpu)
#else
-static u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
+u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
{
u64 idle, idle_usecs = -1ULL;
diff --git a/fs/proc/uptime.c b/fs/proc/uptime.c
index 5a1b228964fb7..deb99bc9b7e6b 100644
--- a/fs/proc/uptime.c
+++ b/fs/proc/uptime.c
@@ -12,18 +12,22 @@ static int uptime_proc_show(struct seq_file *m, void *v)
{
struct timespec64 uptime;
struct timespec64 idle;
- u64 nsec;
+ u64 idle_nsec;
u32 rem;
int i;
- nsec = 0;
- for_each_possible_cpu(i)
- nsec += (__force u64) kcpustat_cpu(i).cpustat[CPUTIME_IDLE];
+ idle_nsec = 0;
+ for_each_possible_cpu(i) {
+ struct kernel_cpustat kcs;
+
+ kcpustat_cpu_fetch(&kcs, i);
+ idle_nsec += get_idle_time(&kcs, i);
+ }
ktime_get_boottime_ts64(&uptime);
timens_add_boottime(&uptime);
- idle.tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
+ idle.tv_sec = div_u64_rem(idle_nsec, NSEC_PER_SEC, &rem);
idle.tv_nsec = rem;
seq_printf(m, "%lu.%02lu %lu.%02lu\n",
(unsigned long) uptime.tv_sec,
diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 89f0745c096d4..8fff3500d50ee 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -103,6 +103,7 @@ extern void account_system_index_time(struct task_struct *, u64,
enum cpu_usage_stat);
extern void account_steal_time(u64);
extern void account_idle_time(u64);
+extern u64 get_idle_time(struct kernel_cpustat *kcs, int cpu);
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
static inline void account_process_tick(struct task_struct *tsk, int user)
--
2.33.0
