From: Douglas Raillard <douglas.raillard@arm.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Viresh Kumar <viresh.kumar@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
qperret@google.com, Linux PM <linux-pm@vger.kernel.org>
Subject: Re: [RFC PATCH v4 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost
Date: Thu, 23 Jan 2020 17:21:05 +0000 [thread overview]
Message-ID: <9b5afae9-0cf5-6c3a-b94b-0796da4e6a71@arm.com> (raw)
In-Reply-To: <CAJZ5v0gP5v3LzU-uGyHpoJV8z+E2heR1PEQp+c=L7RZS3FzCWg@mail.gmail.com>
On 1/23/20 3:55 PM, Rafael J. Wysocki wrote:
> On Wed, Jan 22, 2020 at 6:36 PM Douglas RAILLARD
> <douglas.raillard@arm.com> wrote:
>>
>> Use the utilization signals dynamic to detect when the utilization of a
>> set of tasks starts increasing because of a change in tasks' behavior.
>> This allows detecting when spending extra power for faster frequency
>> ramp up response would be beneficial to the reactivity of the system.
>>
>> This ramp boost is computed as the difference between util_avg and
>> util_est_enqueued. This number somehow represents a lower bound of how
>> much extra utilization this tasks is actually using, compared to our
>> best current stable knowledge of it (which is util_est_enqueued).
>>
>> When the set of runnable tasks changes, the boost is disabled as the
>> impact of blocked utilization on util_avg will make the delta with
>> util_est_enqueued not very informative.
>>
>> Signed-off-by: Douglas RAILLARD <douglas.raillard@arm.com>
>> ---
>> kernel/sched/cpufreq_schedutil.c | 43 ++++++++++++++++++++++++++++++++
>> 1 file changed, 43 insertions(+)
>>
>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>> index 608963da4916..25a410a1ff6a 100644
>> --- a/kernel/sched/cpufreq_schedutil.c
>> +++ b/kernel/sched/cpufreq_schedutil.c
>> @@ -61,6 +61,10 @@ struct sugov_cpu {
>> unsigned long bw_dl;
>> unsigned long max;
>>
>> + unsigned long ramp_boost;
>> + unsigned long util_est_enqueued;
>> + unsigned long util_avg;
>> +
>> /* The field below is for single-CPU policies only: */
>> #ifdef CONFIG_NO_HZ_COMMON
>> unsigned long saved_idle_calls;
>> @@ -183,6 +187,42 @@ 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);
>> +}
>
> Where exactly is this function used?
In the next commit where the boost value is actually used to do
something. The function is introduced here to keep the
WRITE_ONCE/READ_ONCE pair together.
>
>> +
>> +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
>> + * is stable.
>> + */
>> + if (util_est_enqueued == sg_cpu->util_est_enqueued &&
>> + util_avg >= sg_cpu->util_avg &&
>> + util_avg > util_est_enqueued)
>> + boost = util_avg - util_est_enqueued;
>> +
>> + sg_cpu->util_est_enqueued = util_est_enqueued;
>> + sg_cpu->util_avg = util_avg;
>> + WRITE_ONCE(sg_cpu->ramp_boost, boost);
>> + return boost;
>> +}
>> +
>> /**
>> * get_next_freq - Compute a new frequency for a given cpufreq policy.
>> * @sg_policy: schedutil policy object to compute the new frequency for.
>> @@ -514,6 +554,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>> busy = !sg_policy->need_freq_update && sugov_cpu_is_busy(sg_cpu);
>>
>> util = sugov_get_util(sg_cpu);
>> + sugov_cpu_ramp_boost_update(sg_cpu);
>> max = sg_cpu->max;
>> util = sugov_iowait_apply(sg_cpu, time, util, max);
>> next_f = get_next_freq(sg_policy, util, max);
>> @@ -554,6 +595,8 @@ 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);
>> j_max = j_sg_cpu->max;
>> j_util = sugov_iowait_apply(j_sg_cpu, time, j_util, j_max);
>>
>> --
next prev parent reply other threads:[~2020-01-23 17:21 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 17:35 [RFC PATCH v4 0/6] sched/cpufreq: Make schedutil energy aware Douglas RAILLARD
2020-01-22 17:35 ` [RFC PATCH v4 1/6] PM: Introduce em_pd_get_higher_freq() Douglas RAILLARD
2020-01-22 17:35 ` [RFC PATCH v4 2/6] sched/cpufreq: Attach perf domain to sugov policy Douglas RAILLARD
2020-01-22 17:35 ` [RFC PATCH v4 3/6] sched/cpufreq: Hook em_pd_get_higher_power() into get_next_freq() Douglas RAILLARD
2020-01-23 16:16 ` Quentin Perret
2020-01-23 17:52 ` Douglas Raillard
2020-01-24 14:37 ` Quentin Perret
2020-01-24 14:58 ` Quentin Perret
2020-02-27 15:51 ` Douglas Raillard
2020-01-22 17:35 ` [RFC PATCH v4 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost Douglas RAILLARD
2020-01-23 15:55 ` Rafael J. Wysocki
2020-01-23 17:21 ` Douglas Raillard [this message]
2020-01-23 21:02 ` Rafael J. Wysocki
2020-01-28 15:38 ` Douglas Raillard
2020-02-10 13:08 ` Peter Zijlstra
2020-02-13 10:49 ` Douglas Raillard
2020-01-22 17:35 ` [RFC PATCH v4 5/6] sched/cpufreq: Boost schedutil frequency ramp up Douglas RAILLARD
2020-01-22 17:35 ` [RFC PATCH v4 6/6] sched/cpufreq: Add schedutil_em_tp tracepoint Douglas RAILLARD
2020-01-22 18:14 ` [RFC PATCH v4 0/6] sched/cpufreq: Make schedutil energy aware Douglas Raillard
2020-02-10 13:21 ` Peter Zijlstra
2020-02-13 17:49 ` Douglas Raillard
2020-02-14 12:21 ` Peter Zijlstra
2020-02-14 12:52 ` Peter Zijlstra
2020-03-11 12:25 ` Douglas Raillard
2020-02-14 13:37 ` Peter Zijlstra
2020-03-11 12:40 ` Douglas Raillard
2020-01-23 15:43 ` Rafael J. Wysocki
2020-01-23 17:16 ` Douglas Raillard
2020-02-10 13:30 ` Peter Zijlstra
2020-02-13 11:55 ` Douglas Raillard
2020-02-13 13:20 ` Peter Zijlstra
2020-02-27 15:50 ` Douglas Raillard
2020-01-27 17:16 ` Vincent Guittot
2020-02-10 11:37 ` Douglas Raillard
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