linux-kernel - Re: [RFC PATCH v3 4/6] sched/cpufreq: Introduce sugov_cpu_ramp

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Date:   Thu, 17 Oct 2019 10:57:19 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Douglas RAILLARD <douglas.raillard@....com>,
        linux-kernel@...r.kernel.org
Cc:     linux-pm@...r.kernel.org, mingo@...hat.com, peterz@...radead.org,
        rjw@...ysocki.net, viresh.kumar@...aro.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, qperret@...rret.net,
        patrick.bellasi@...bug.net, dh.han@...sung.com
Subject: Re: [RFC PATCH v3 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost

On 11/10/2019 15:44, Douglas RAILLARD wrote:

[...]

> @@ -181,6 +185,42 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy, u64 time,
>  	}
>  }
>  
> +static unsigned long sugov_cpu_ramp_boost(struct sugov_cpu *sg_cpu)
> +{
> +	return READ_ONCE(sg_cpu->ramp_boost);
> +}
> +
> +static unsigned long sugov_cpu_ramp_boost_update(struct sugov_cpu *sg_cpu)
> +{
> +	struct rq *rq = cpu_rq(sg_cpu->cpu);
> +	unsigned long util_est_enqueued;
> +	unsigned long util_avg;
> +	unsigned long boost = 0;
> +
> +	util_est_enqueued = READ_ONCE(rq->cfs.avg.util_est.enqueued);
> +	util_avg = READ_ONCE(rq->cfs.avg.util_avg);
> +
> +	/*
> +	 * Boost when util_avg becomes higher than the previous stable
> +	 * knowledge of the enqueued tasks' set util, which is CPU's
> +	 * util_est_enqueued.
> +	 *
> +	 * We try to spot changes in the workload itself, so we want to
> +	 * avoid the noise of tasks being enqueued/dequeued. To do that,
> +	 * we only trigger boosting when the "amount of work' enqueued

s/"amount of work'/"amount of work" or 'amount of work'

[...]

> @@ -552,6 +593,8 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
>  		unsigned long j_util, j_max;
>  
>  		j_util = sugov_get_util(j_sg_cpu);
> +		if (j_sg_cpu == sg_cpu)
> +			sugov_cpu_ramp_boost_update(sg_cpu);

Can you not call this already in sugov_update_shared(), like in the
sugov_update_single() case?

diff --git a/kernel/sched/cpufreq_schedutil.c
b/kernel/sched/cpufreq_schedutil.c
index e35c20b42780..4c53f63a537d 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -595,8 +595,6 @@ static unsigned int sugov_next_freq_shared(struct
sugov_cpu *sg_cpu, u64 time)
                unsigned long j_util, j_max;

                j_util = sugov_get_util(j_sg_cpu);
-               if (j_sg_cpu == sg_cpu)
-                       sugov_cpu_ramp_boost_update(sg_cpu);
                j_max = j_sg_cpu->max;
                j_util = sugov_iowait_apply(j_sg_cpu, time, j_util, j_max);

@@ -625,6 +623,7 @@ sugov_update_shared(struct update_util_data *hook,
u64 time, unsigned int flags)
        ignore_dl_rate_limit(sg_cpu, sg_policy);

        if (sugov_should_update_freq(sg_policy, time)) {
+               sugov_cpu_ramp_boost_update(sg_cpu);
                next_f = sugov_next_freq_shared(sg_cpu, time);

[...]