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author | Michal Hocko <mhocko@suse.cz> | 2011-12-08 22:34:32 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-12-09 15:50:29 (GMT) |
commit | 2a95ea6c0d129b4568fb64e1deda16ceb20e6636 (patch) | |
tree | 0648fbd539e00fcfc4a394acaabd3e54b4bf8658 | |
parent | 1368edf0647ac112d8cfa6ce47257dc950c50f5c (diff) | |
download | linux-2a95ea6c0d129b4568fb64e1deda16ceb20e6636.tar.xz |
procfs: do not overflow get_{idle,iowait}_time for nohz
Since commit a25cac5198d4 ("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>
-rw-r--r-- | fs/proc/stat.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/proc/stat.c b/fs/proc/stat.c index 42b274d..2a30d67 100644 --- a/fs/proc/stat.c +++ b/fs/proc/stat.c @@ -32,7 +32,7 @@ static cputime64_t get_idle_time(int cpu) idle = kstat_cpu(cpu).cpustat.idle; idle = cputime64_add(idle, arch_idle_time(cpu)); } else - idle = usecs_to_cputime(idle_time); + idle = nsecs_to_jiffies64(1000 * idle_time); return idle; } @@ -46,7 +46,7 @@ static cputime64_t get_iowait_time(int cpu) /* !NO_HZ so we can rely on cpustat.iowait */ iowait = kstat_cpu(cpu).cpustat.iowait; else - iowait = usecs_to_cputime(iowait_time); + iowait = nsecs_to_jiffies64(1000 * iowait_time); return iowait; } |