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proc: Consider NO_HZ when printing idle and iowait times 

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accounting while we are tickless so the value might get outdated.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: Alexey Dobriyan <adobriyan@gmail.com>
Link: http://lkml.kernel.org/r/39181366adac1b39cb6aa3cd53ff0f7c78d32676.1314172057.git.mhocko@suse.cz
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Michal Hocko 2011-08-24 09:40:25 +02:00 committed by Thomas Gleixner
parent 09a1d34f85
commit a25cac5198
1 changed files with 34 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
fs/proc/stat.c
View File

@ -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;