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    Subject[PATCH] sched: cpufreq: Rename map_util_perf to apply_dvfs_headroom
    Date
    We are providing headroom for the utilization to grow until the next
    decision point to pick the next frequency. Give the function a better
    name and give it some documentation. It is not really mapping anything.

    Also move it to sched.h. This function relies on updating util signal
    appropriately to give a headroom to grow. This is more of a scheduler
    functionality than cpufreq. Move it to sched.h where all the other util
    handling code belongs.

    Signed-off-by: Qais Yousef <qyousef@layalina.io>
    ---
    include/linux/sched/cpufreq.h | 5 -----
    kernel/sched/cpufreq_schedutil.c | 2 +-
    kernel/sched/sched.h | 17 +++++++++++++++++
    3 files changed, 18 insertions(+), 6 deletions(-)

    diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
    index bdd31ab93bc5..d01755d3142f 100644
    --- a/include/linux/sched/cpufreq.h
    +++ b/include/linux/sched/cpufreq.h
    @@ -28,11 +28,6 @@ static inline unsigned long map_util_freq(unsigned long util,
    {
    return freq * util / cap;
    }
    -
    -static inline unsigned long map_util_perf(unsigned long util)
    -{
    - return util + (util >> 2);
    -}
    #endif /* CONFIG_CPU_FREQ */

    #endif /* _LINUX_SCHED_CPUFREQ_H */
    diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
    index 95c3c097083e..abbd1ddb0359 100644
    --- a/kernel/sched/cpufreq_schedutil.c
    +++ b/kernel/sched/cpufreq_schedutil.c
    @@ -179,7 +179,7 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
    unsigned long max)
    {
    /* Add dvfs headroom to actual utilization */
    - actual = map_util_perf(actual);
    + actual = apply_dvfs_headroom(actual);
    /* Actually we don't need to target the max performance */
    if (actual < max)
    max = actual;
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index e58a54bda77d..0da3425200b1 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -3002,6 +3002,23 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
    unsigned long min,
    unsigned long max);

    +/*
    + * DVFS decision are made at discrete points. If CPU stays busy, the util will
    + * continue to grow, which means it could need to run at a higher frequency
    + * before the next decision point was reached. IOW, we can't follow the util as
    + * it grows immediately, but there's a delay before we issue a request to go to
    + * higher frequency. The headroom caters for this delay so the system continues
    + * to run at adequate performance point.
    + *
    + * This function provides enough headroom to provide adequate performance
    + * assuming the CPU continues to be busy.
    + *
    + * At the moment it is a constant multiplication with 1.25.
    + */
    +static inline unsigned long apply_dvfs_headroom(unsigned long util)
    +{
    + return util + (util >> 2);
    +}

    /*
    * Verify the fitness of task @p to run on @cpu taking into account the
    --
    2.34.1

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