On Fri, 22 Jun 2018 at 17:23, Peter Zijlstra <[email protected]> wrote:
>
> 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.
good point
>
> --- 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) {
>
