From: Josh Don joshdon@google.com
[ 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@google.com Signed-off-by: Josh Don joshdon@google.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Eric Dumazet edumazet@google.com Link: https://lkml.kernel.org/r/20210827165438.3280779-1-joshdon@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 6561a06ef9059..4fb8729a68d4e 100644 --- a/fs/proc/stat.c +++ b/fs/proc/stat.c @@ -24,7 +24,7 @@
#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;
@@ -46,7 +46,7 @@ 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 44ae1a7eb9e39..69ae6b2784645 100644 --- a/include/linux/kernel_stat.h +++ b/include/linux/kernel_stat.h @@ -102,6 +102,7 @@ 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)