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  • 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 disab...
    62d6ae88