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Michal Hocko 2a95ea6c0d procfs: do not overflow get_{idle,iowait}_time for nohz 
Since commit a25cac5198 ("proc: Consider NO_HZ when printing idle and
iowait times") we are reporting idle/io_wait time also while a CPU is
tickless.  We rely on get_{idle,iowait}_time functions to retrieve
proper data.

These functions, however, use usecs_to_cputime to translate micro
seconds time to cputime64_t.  This is just an alias to usecs_to_jiffies
which reduces the data type from u64 to unsigned int and also checks
whether the given parameter overflows jiffies_to_usecs(MAX_JIFFY_OFFSET)
and returns MAX_JIFFY_OFFSET in that case.

When we overflow depends on CONFIG_HZ but especially for CONFIG_HZ_300
it is quite low (1431649781) so we are getting MAX_JIFFY_OFFSET for
>3000s! until we overflow unsigned int.  Just for reference
CONFIG_HZ_100 has an overflow window around 20s, CONFIG_HZ_250 ~8s and
CONFIG_HZ_1000 ~2s.

This results in a bug when people saw [h]top going mad reporting 100%
CPU usage even though there was basically no CPU load.  The reason was
simply that /proc/stat stopped reporting idle/io_wait changes (and
reported MAX_JIFFY_OFFSET) and so the only change happening was for user
system time.

Let's use nsecs_to_jiffies64 instead which doesn't reduce the precision
to 32b type and it is much more appropriate for cumulative time values
(unlike usecs_to_jiffies which intended for timeout calculations).

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Tested-by: Artem S. Tashkinov <t.artem@mailcity.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2011-12-09 07:50:29 -08:00
..
Kconfig
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Makefile ns: proc files for namespace naming policy. 2011-05-10 14:31:44 -07:00
array.c ptrace: s/tracehook_tracer_task()/ptrace_parent()/ 2011-06-22 19:26:29 +02:00
base.c Revert "proc: fix races against execve() of /proc/PID/fd**" 2011-11-09 18:16:00 -05:00
cmdline.c
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consoles.c
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cpuinfo.c
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devices.c
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generic.c filesystems: add set_nlink() 2011-11-02 12:53:43 +01:00
inode.c filesystems: add set_nlink() 2011-11-02 12:53:43 +01:00
internal.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/linux-2.6-nsfd 2011-05-25 18:10:16 -07:00
interrupts.c
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kcore.c
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kmsg.c
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loadavg.c
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meminfo.c fs/proc/meminfo.c: fix compilation error 2011-12-09 07:50:28 -08:00
mmu.c
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namespaces.c proc: Fix Oops on stat of /proc/<zombie pid>/ns/net 2011-06-15 14:35:29 -07:00
nommu.c
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page.c
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proc_devtree.c of/flattree: Drop an uninteresting message to pr_debug level 2011-03-02 13:45:18 -07:00
proc_net.c proc: make struct proc_dir_entry::name a terminal array rather than a pointer 2011-07-27 12:50:45 -07:00
proc_sysctl.c Merge branch 'akpm' (Andrew's incoming - part two) 2011-11-02 16:07:27 -07:00
proc_tty.c
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root.c proc: make struct proc_dir_entry::name a terminal array rather than a pointer 2011-07-27 12:50:45 -07:00
softirqs.c
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stat.c procfs: do not overflow get_{idle,iowait}_time for nohz 2011-12-09 07:50:29 -08:00
task_mmu.c mm: distinguish between mlocked and pinned pages 2011-10-31 17:30:46 -07:00
task_nommu.c report errors in /proc/*/*map* sanely 2011-03-23 16:36:50 -04:00
uptime.c
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version.c
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vmcore.c fs: add export.h to files using EXPORT_SYMBOL/THIS_MODULE macros 2011-10-31 19:30:31 -04:00