[PATCH] proc: consider time when ticks are off when reporting idletime

[Michal Hocko]

---
 fs/proc/stat.c           |    3 +++
 kernel/time/tick-sched.c |   20 ++++++++++++++++++++
 2 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 9758b65..970ec81 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -21,6 +21,8 @@
 #define arch_idle_time(cpu) 0
 #endif
 
+cputime64_t nohz_idle_shift(int cpu);
+
 static int show_stat(struct seq_file *p, void *v)
 {
 	int i, j;
@@ -44,6 +46,7 @@ static int show_stat(struct seq_file *p, void *v)
 		system = cputime64_add(system, kstat_cpu(i).cpustat.system);
 		idle = cputime64_add(idle, kstat_cpu(i).cpustat.idle);
 		idle = cputime64_add(idle, arch_idle_time(i));
+		idle = cputime64_add(idle, nohz_idle_shift(i));
 		iowait = cputime64_add(iowait, kstat_cpu(i).cpustat.iowait);
 		irq = cputime64_add(irq, kstat_cpu(i).cpustat.irq);
 		softirq = cputime64_add(softirq, kstat_cpu(i).cpustat.softirq);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index d5097c4..57d11fa 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -194,6 +194,26 @@ static ktime_t tick_nohz_start_idle(int cpu, struct tick_sched *ts)
 	return now;
 }
 
+cputime64_t nohz_idle_shift(int cpu)
+{
+	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+	cputime64_t notick_idle = 0;
+
+	if (ts->idle_active && time_after(ts->next_jiffies, jiffies)) {
+		/*
+		 * we are idle and not ticking due to NOHZ so the
+		 * kernel doesn't account for the idle. Let's use
+		 * last_jiffies. We are screwed when jiffies overflow
+		 * of course but what else we can do?
+		 */
+		notick_idle = cputime64_add(notick_idle,
+				jiffies_to_cputime(
+					jiffies - ts->last_jiffies));
+	}
+
+	return notick_idle;
+}
+
 /**
  * get_cpu_idle_time_us - get the total idle time of a cpu
  * @cpu: CPU number to query
-- 
1.7.5.4


-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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