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    SubjectRe: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking
    On Fri, Jun 22, 2018 at 01:37:13PM +0200, Peter Zijlstra wrote:
    > That is true.. So we could limit the scaling to the case where there is
    > no idle time, something like:
    >
    > util = sg_cpu->util_cfs;
    >
    > cap_cfs = (1024 - (sg_cpu->util_rt + ...));
    > if (util == cap_cfs)
    > util = sg_cpu->max;
    >

    OK, it appears this is more or less what the patches do. And I think
    there's a small risk/hole with this where util ~= cap_cfs but very close
    due to some unaccounted time.

    FWIW, when looking, I saw no reason why sugov_get_util() and
    sugov_aggregate_util() were in fact separate functions.

    --- a/kernel/sched/cpufreq_schedutil.c
    +++ b/kernel/sched/cpufreq_schedutil.c
    @@ -53,11 +53,7 @@ struct sugov_cpu {
    unsigned int iowait_boost_max;
    u64 last_update;

    - /* The fields below are only needed when sharing a policy: */
    - unsigned long util_cfs;
    unsigned long util_dl;
    - unsigned long bw_dl;
    - unsigned long util_rt;
    unsigned long max;

    /* The field below is for single-CPU policies only: */
    @@ -181,44 +177,38 @@ static unsigned int get_next_freq(struct
    return cpufreq_driver_resolve_freq(policy, freq);
    }

    -static void sugov_get_util(struct sugov_cpu *sg_cpu)
    +static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
    {
    struct rq *rq = cpu_rq(sg_cpu->cpu);
    + unsigned long util, max;

    - sg_cpu->max = arch_scale_cpu_capacity(NULL, sg_cpu->cpu);
    - sg_cpu->util_cfs = cpu_util_cfs(rq);
    - sg_cpu->util_dl = cpu_util_dl(rq);
    - sg_cpu->bw_dl = cpu_bw_dl(rq);
    - sg_cpu->util_rt = cpu_util_rt(rq);
    -}
    -
    -static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
    -{
    - struct rq *rq = cpu_rq(sg_cpu->cpu);
    - unsigned long util;
    + sg_cpu->max = max = arch_scale_cpu_capacity(NULL, sg_cpu->cpu);
    + sg_cpu->util_dl = cpu_util_dl(rq);

    if (rq->rt.rt_nr_running)
    - return sg_cpu->max;
    + return max;

    - util = sg_cpu->util_cfs;
    - util += sg_cpu->util_rt;
    + util = cpu_util_cfs(rq);
    + util += cpu_util_rt(rq);

    - if ((util + sg_cpu->util_dl) >= sg_cpu->max)
    - return sg_cpu->max;
    + /*
    + * If there is no idle time, we should run at max frequency.
    + */
    + if ((util + cpu_util_dl(rq)) >= max)
    + return max;

    /*
    - * As there is still idle time on the CPU, we need to compute the
    - * utilization level of the CPU.
    * Bandwidth required by DEADLINE must always be granted while, for
    * FAIR and RT, we use blocked utilization of IDLE CPUs as a mechanism
    * to gracefully reduce the frequency when no tasks show up for longer
    * periods of time.
    + *
    + * Ideally we would like to set bw_dl as min/guaranteed freq and bw_dl
    + * + util as requested freq. However, cpufreq is not yet ready for such
    + * an interface. So, we only do the latter for now.
    */

    - /* Add DL bandwidth requirement */
    - util += sg_cpu->bw_dl;
    -
    - return min(sg_cpu->max, util);
    + return min(max, cpu_bw_dl(rq) + util);
    }

    /**
    @@ -396,9 +386,8 @@ static void sugov_update_single(struct u

    busy = sugov_cpu_is_busy(sg_cpu);

    - sugov_get_util(sg_cpu);
    + util = sugov_get_util(sg_cpu);
    max = sg_cpu->max;
    - util = sugov_aggregate_util(sg_cpu);
    sugov_iowait_apply(sg_cpu, time, &util, &max);
    next_f = get_next_freq(sg_policy, util, max);
    /*
    @@ -437,9 +426,8 @@ static unsigned int sugov_next_freq_shar
    struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j);
    unsigned long j_util, j_max;

    - sugov_get_util(j_sg_cpu);
    + j_util = sugov_get_util(j_sg_cpu);
    j_max = j_sg_cpu->max;
    - j_util = sugov_aggregate_util(j_sg_cpu);
    sugov_iowait_apply(j_sg_cpu, time, &j_util, &j_max);

    if (j_util * max > j_max * util) {
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      Last update: 2018-06-22 17:23    [W:4.344 / U:0.236 seconds]
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