show_stat handler of the /proc/stat file relies on kstat_cpu(cpu)

statistics when priting information about idle and iowait times.  This is
OK if we are not using tickless kernel (CONFIG_NO_HZ) because counters are
updated periodically.

With NO_HZ things got more tricky because we are not doing idle/iowait
accounting while we are tickless so the value might get outdated.  Users
of /proc/stat will notice that by unchanged idle/iowait values which is
then interpreted as 0% idle/iowait time.  From the user space POV this is
an unexpected behavior and a change of the interface.

Let's fix this by using get_cpu_{idle,iowait}_time_us which accounts the
total idle/iowait time since boot and it doesn't rely on sampling or any
other periodic activity.  Fall back to the previous behavior if NO_HZ is
disabled or not configured.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Cc: Dave Jones <davej@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 9758b654a1bcffe27c414ef322f34cd6a8658c33..42b274da92c39d539c7c2f0f82a2f825c1a20383 100644 (file)
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -10,6 +10,7 @@
 #include <linux/time.h>
 #include <linux/irqnr.h>
 #include <asm/cputime.h>
+#include <linux/tick.h>
 
 #ifndef arch_irq_stat_cpu
 #define arch_irq_stat_cpu(cpu) 0
@@ -21,6 +22,35 @@
 #define arch_idle_time(cpu) 0
 #endif
 
+static cputime64_t get_idle_time(int cpu)
+{
+       u64 idle_time = get_cpu_idle_time_us(cpu, NULL);
+       cputime64_t idle;
+
+       if (idle_time == -1ULL) {
+               /* !NO_HZ so we can rely on cpustat.idle */
+               idle = kstat_cpu(cpu).cpustat.idle;
+               idle = cputime64_add(idle, arch_idle_time(cpu));
+       } else
+               idle = usecs_to_cputime(idle_time);
+
+       return idle;
+}
+
+static cputime64_t get_iowait_time(int cpu)
+{
+       u64 iowait_time = get_cpu_iowait_time_us(cpu, NULL);
+       cputime64_t iowait;
+
+       if (iowait_time == -1ULL)
+               /* !NO_HZ so we can rely on cpustat.iowait */
+               iowait = kstat_cpu(cpu).cpustat.iowait;
+       else
+               iowait = usecs_to_cputime(iowait_time);
+
+       return iowait;
+}
+
 static int show_stat(struct seq_file *p, void *v)
 {
        int i, j;
@@ -42,9 +72,8 @@ static int show_stat(struct seq_file *p, void *v)
                user = cputime64_add(user, kstat_cpu(i).cpustat.user);
                nice = cputime64_add(nice, kstat_cpu(i).cpustat.nice);
                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));
-               iowait = cputime64_add(iowait, kstat_cpu(i).cpustat.iowait);
+               idle = cputime64_add(idle, get_idle_time(i));
+               iowait = cputime64_add(iowait, get_iowait_time(i));
                irq = cputime64_add(irq, kstat_cpu(i).cpustat.irq);
                softirq = cputime64_add(softirq, kstat_cpu(i).cpustat.softirq);
                steal = cputime64_add(steal, kstat_cpu(i).cpustat.steal);
@@ -76,14 +105,12 @@ static int show_stat(struct seq_file *p, void *v)
                (unsigned long long)cputime64_to_clock_t(guest),
                (unsigned long long)cputime64_to_clock_t(guest_nice));
        for_each_online_cpu(i) {
-
                /* Copy values here to work around gcc-2.95.3, gcc-2.96 */
                user = kstat_cpu(i).cpustat.user;
                nice = kstat_cpu(i).cpustat.nice;
                system = kstat_cpu(i).cpustat.system;
-               idle = kstat_cpu(i).cpustat.idle;
-               idle = cputime64_add(idle, arch_idle_time(i));
-               iowait = kstat_cpu(i).cpustat.iowait;
+               idle = get_idle_time(i);
+               iowait = get_iowait_time(i);
                irq = kstat_cpu(i).cpustat.irq;
                softirq = kstat_cpu(i).cpustat.softirq;
                steal = kstat_cpu(i).cpustat.steal;