Commit a130e8fb authored by Josh Don's avatar Josh Don Committed by Peter Zijlstra
Browse files

fs/proc/uptime.c: Fix idle time reporting in /proc/uptime 



/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: default avatarLuigi Rizzo <lrizzo@google.com>
Signed-off-by: default avatarJosh Don <joshdon@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://lkml.kernel.org/r/20210827165438.3280779-1-joshdon@google.com
parent bc9ffef3

fs/proc/stat.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

fs/proc/uptime.c

+9 −5
Original line number Diff line number Diff line
@@ -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,

include/linux/kernel_stat.h

+1 −0
Original line number Diff line number Diff line
@@ -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)