* + proc-consider-no_hz-when-printing-idle-and-iowait-times.patch added to -mm tree
@ 2011-08-24 18:59 akpm
0 siblings, 0 replies; only message in thread
From: akpm @ 2011-08-24 18:59 UTC (permalink / raw)
To: mm-commits; +Cc: mhocko, adobriyan, arnd, davej, tglx
The patch titled
proc: consider NO_HZ when printing idle and iowait times
has been added to the -mm tree. Its filename is
proc-consider-no_hz-when-printing-idle-and-iowait-times.patch
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------------------------------------------------------
Subject: proc: consider NO_HZ when printing idle and iowait times
From: Michal Hocko <mhocko@suse.cz>
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accounting while we are tickless so the value might get outdated.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>
---
fs/proc/stat.c | 41 ++++++++++++++++++++++++++++++++++-------
1 file changed, 34 insertions(+), 7 deletions(-)
diff -puN fs/proc/stat.c~proc-consider-no_hz-when-printing-idle-and-iowait-times fs/proc/stat.c
--- a/fs/proc/stat.c~proc-consider-no_hz-when-printing-idle-and-iowait-times
+++ a/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,
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,
(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;
_
Patches currently in -mm which might be from mhocko@suse.cz are
memcg-pin-execution-to-current-cpu-while-draining-stock.patch
memcg-make-oom_lock-0-and-1-based-rather-than-coutner.patch
linux-next.patch
cputime-clean-up-cputime_to_usecs-and-usecs_to_cputime-macros.patch
tick-fix-update_ts_time_stat-idle-accounting.patch
nohz-do-not-update-idle-iowait-counters-from-get_cpu_idleiowait_time_us-if-not-asked.patch
proc-consider-no_hz-when-printing-idle-and-iowait-times.patch
mm-compaction-trivial-clean-up-in-acct_isolated.patch
mm-change-isolate-mode-from-define-to-bitwise-type.patch
mm-compaction-make-isolate_lru_page-filter-aware.patch
mm-zone_reclaim-make-isolate_lru_page-filter-aware.patch
mm-migration-clean-up-unmap_and_move.patch
mm-page-writebackc-make-determine_dirtyable_memory-static-again.patch
oom-avoid-killing-kthreads-if-they-assume-the-oom-killed-threads-mm.patch
mm-vmscan-fix-force-scanning-small-targets-without-swap.patch
mm-vmscan-drop-nr_force_scan-from-get_scan_count.patch
memcg-rename-mem-variable-to-memcg.patch
memcg-fix-oom-schedule_timeout.patch
memcg-do-not-expose-uninitialized-mem_cgroup_per_node-to-world.patch
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2011-08-24 18:59 + proc-consider-no_hz-when-printing-idle-and-iowait-times.patch added to -mm tree akpm
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