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Commit a25cac51 authored by Michal Hocko's avatar Michal Hocko Committed by Thomas Gleixner
Browse files

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accounting while we are tickless so the value might get outdated.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: default avatarMichal 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: default avatarThomas Gleixner <tglx@linutronix.de>
parent 09a1d34f

fs/proc/stat.c

+34 −7
Original line number Diff line number Diff line
@@ -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;