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Michal Hocko authored
Since commit a25cac51 ("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>
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