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    SubjectRe: [RFC PATCH 3/3] idle: store the idle state index in the struct rq
    Hi Peter,

    On 01/31/2014 02:32 PM, Peter Zijlstra wrote:
    > On Fri, Jan 31, 2014 at 02:15:47PM +0530, Preeti Murthy wrote:
    >>>
    >>> If the driver does its own random mapping that will break the governor
    >>> logic. So yes, the states are ordered, the higher the index is, the more you
    >>> save power and the higher the exit latency is.
    >>
    >> The above point holds true for only the ladder governor which sees the idle
    >> states indexed in the increasing order of target_residency/exit_latency.
    >>
    >> However this is not true as far as I can see in the menu governor. It
    >> acknowledges the dynamic ordering of idle states as can be seen in the
    >> menu_select() function in the menu governor, where the idle state for the
    >> CPU gets chosen. You will notice that, even if it is found that the predicted
    >> idle time of the CPU is smaller than the target residency of an idle state,
    >> the governor continues to search for suitable idle states in the higher indexed
    >> states although it should have halted if the idle states' were ordered according
    >> to their target residency.. The same holds for exit_latency.
    >>
    >> Hence I think this patch would make sense only with additional information
    >> like exit_latency or target_residency is present for the scheduler. The idle
    >> state index alone will not be sufficient.
    >
    > Alternatively, can we enforce sanity on the cpuidle infrastructure to
    > make the index naturally ordered? If not, please explain why :-)

    The commit id 71abbbf856a0e70 says that there are SOCs which could have
    their target_residency and exit_latency values change at runtime. This
    commit thus removed the ordering of the idle states according to their
    target_residency/exit_latency. Adding Len and Arjan to the CC.

    Thanks

    Regards
    Preeti U Murthy

    >



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