• Carsten Emde's avatar
    Honor state disabling in the cpuidle ladder governor · 62d6ae88
    Carsten Emde authored
    There are two cpuidle governors ladder and menu. While the ladder
    governor is always available, if CONFIG_CPU_IDLE is selected, the
    menu governor additionally requires CONFIG_NO_HZ.
    A particular C state can be disabled by writing to the sysfs file
    /sys/devices/system/cpu/cpuN/cpuidle/stateN/disable, but this mechanism
    is only implemented in the menu governor. Thus, in a system where
    CONFIG_NO_HZ is not selected, the ladder governor becomes default and
    always will walk through all sleep states - irrespective of whether the
    C state was disabled via sysfs or not. The only way to select a specific
    C state was to write the related latency to /dev/cpu_dma_latency and
    keep the file open as long as this setting was required - not very
    practical and not suitable for setting a single core in an SMP system.
    With this patch, the ladder governor only will promote to the next
    C state, if it has not been disabled, and it will demote, if the
    current C state was disabled.
    Note that the patch does not make the setting of the sysfs variable
    "disable" coherent, i.e. if one is disabling a light state, then all
    deeper states are disabled as well, but the "disable" variable does not
    reflect it. Likewise, if one enables a deep state but a lighter state
    still is disabled, then this has no effect. A related section has been
    added to the documentation.
    Signed-off-by: default avatarCarsten Emde <C.Emde@osadl.org>
    Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
sysfs.txt 3.37 KB