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    SubjectRe: [PATCH v3 0/3] cpufreq: avoid redundant driver calls in schedutil
    On 13-07-16, 13:25, Steve Muckle wrote:
    > Invoking the cpufreq driver to set a frequency can be expensive. On platforms
    > with a cpufreq driver that does not support fast switching a thread must be
    > woken to complete the operation. IPIs will also occur if and when support to
    > process remote task wakeups is added in schedutil.
    >
    > Currently schedutil calculates a raw frequency request from scheduler
    > utilization data. This raw frequency request does not correlate to supported
    > cpufreq driver frequencies aside from being capped by the CPU's maximum
    > frequency. Consequently, there may be many consecutive requests for different
    > raw frequency values which all translate to the same driver-supported
    > frequency. For example on a platform with 3 supported frequencies 200MHz,
    > 400MHz, and 600MHz, raw requests for 257MHz, 389MHz, and 307MHz all map to a
    > driver-supported frequency of 400MHz in schedutil. Assuming these requests were
    > consecutive and there were no changes in policy limits (min/max), there is no
    > need to issue the second or third request.
    >
    > In order to resolve a raw frequency request to a driver-supported one a new
    > cpufreq API is added, cpufreq_driver_resolve_freq(). This API relies on a new
    > cpufreq driver callback in the case of ->target() style drivers. Otherwise it
    > uses the existing frequency table operations.
    >
    > Lookups are cached both in cpufreq_driver_resolve_freq() (for the benefit of the
    > driver) and in schedutil.
    >
    > Changes since v2:
    > - incorporated feedback from Viresh to use resolve_freq driver callbacks
    > only for ->target() style drivers, to use cpufreq's freq table operations,
    > and move freq mapping caching into cpufreq policy

    Sorry for the delay buddy :(

    I have some concerns for the first patch. The second and third patch
    look fine. Feel free to add my

    Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>

    for them.

    --
    viresh

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