• Michal Hocko's avatar
    proc: Consider NO_HZ when printing idle and iowait times · a25cac51
    Michal Hocko authored
    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    accounting while we are tickless so the value might get outdated.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.czSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    a25cac51
stat.c 5.4 KB