Eric Lee / smarc-ti-linux-kernel

04 Sep, 2012

1 commit

  • 62d6ae880   Honor state disabling in the cpuidle ladder governor ... Browse Code »

    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: Carsten Emde
    Signed-off-by: Rafael J. Wysocki

    Carsten Emde
     

30 Mar, 2012

1 commit

  • 3a53396b0   cpuidle: add a sysfs entry to disable specific C state for debug purpose. ... Browse Code »

    Some C states of new CPU might be not good. One reason is BIOS might
    configure them incorrectly. To help developers root cause it quickly, the
    patch adds a new sysfs entry, so developers could disable specific C state
    manually.

    In addition, C state might have much impact on performance tuning, as it
    takes much time to enter/exit C states, which might delay interrupt
    processing. With the new debug option, developers could check if a deep C
    state could impact performance and how much impact it could cause.

    Also add this option in Documentation/cpuidle/sysfs.txt.

    [akpm@linux-foundation.org: check kstrtol return value]
    Signed-off-by: ShuoX Liu
    Reviewed-by: Yanmin Zhang
    Reviewed-and-Tested-by: Deepthi Dharwar
    Signed-off-by: Andrew Morton
    Signed-off-by: Len Brown

    ShuoX Liu
     

14 Feb, 2008

1 commit