On Thu, Aug 12, 2021 at 10:31 PM Josh Don <joshdon@xxxxxxxxxx> wrote:
>
> /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>
> ---
> fs/proc/stat.c | 26 --------------------------
> fs/proc/uptime.c | 13 ++++++++-----
> include/linux/kernel_stat.h | 1 +
> kernel/sched/cputime.c | 28 ++++++++++++++++++++++++++++
> 4 files changed, 37 insertions(+), 31 deletions(-)
>
> diff --git a/fs/proc/stat.c b/fs/proc/stat.c
> index 6561a06ef905..99796a8a5223 100644
> --- a/fs/proc/stat.c
> +++ b/fs/proc/stat.c
> @@ -24,16 +24,6 @@
>
> #ifdef arch_idle_time
>
> -static u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
> -{
> - u64 idle;
> -
> - idle = kcs->cpustat[CPUTIME_IDLE];
> - if (cpu_online(cpu) && !nr_iowait_cpu(cpu))
> - idle += arch_idle_time(cpu);
> - return idle;
> -}
> -
> static u64 get_iowait_time(struct kernel_cpustat *kcs, int cpu)
> {
> u64 iowait;
> @@ -46,22 +36,6 @@ static u64 get_iowait_time(struct kernel_cpustat *kcs, int cpu)
>
> #else
>
> -static u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
> -{
> - u64 idle, idle_usecs = -1ULL;
> -
> - if (cpu_online(cpu))
> - idle_usecs = get_cpu_idle_time_us(cpu, NULL);
> -
> - if (idle_usecs == -1ULL)
> - /* !NO_HZ or cpu offline so we can rely on cpustat.idle */
> - idle = kcs->cpustat[CPUTIME_IDLE];
> - else
> - idle = idle_usecs * NSEC_PER_USEC;
> -
> - return idle;
> -}
> -
> static u64 get_iowait_time(struct kernel_cpustat *kcs, int cpu)
> {
> u64 iowait, iowait_usecs = -1ULL;
...
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 872e481d5098..9d7629e21164 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -227,6 +227,34 @@ void account_idle_time(u64 cputime)
> cpustat[CPUTIME_IDLE] += cputime;
> }
>
> +/*
> + * Returns the total idle time for the given cpu.
> + * @kcs: The kernel_cpustat for the desired cpu.
> + * @cpu: The desired cpu.
> + */
> +u64 get_idle_time(const struct kernel_cpustat *kcs, int cpu)
> +{
> + u64 idle;
> + u64 __maybe_unused idle_usecs = -1ULL;
> +
> +#ifdef arch_idle_time
> + idle = kcs->cpustat[CPUTIME_IDLE];
> + if (cpu_online(cpu) && !nr_iowait_cpu(cpu))
> + idle += arch_idle_time(cpu);
> +#else
> + if (cpu_online(cpu))
> + idle_usecs = get_cpu_idle_time_us(cpu, NULL);
> +
> + if (idle_usecs == -1ULL)
> + /* !NO_HZ or cpu offline so we can rely on cpustat.idle */
> + idle = kcs->cpustat[CPUTIME_IDLE];
> + else
> + idle = idle_usecs * NSEC_PER_USEC;
> +#endif
> +
> + return idle;
> +}
> +
>
Not sure why you moved get_idle_time() in kernel/sched/cputime.c
For builds where CONFIG_PROC_FS is not set, this function is not used/needed.
