linux-kernel - Re: [PATCH v3] cpufreq: schedutil: rate limits for SCHED

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Date:   Thu, 8 Mar 2018 12:13:01 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Claudio Scordino <claudio@...dence.eu.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] cpufreq: schedutil: rate limits for SCHED_DEADLINE

On Thu, Mar 8, 2018 at 11:29 AM, Claudio Scordino
<claudio@...dence.eu.com> wrote:
> When the SCHED_DEADLINE scheduling class increases the CPU utilization,
> we should not wait for the rate limit, otherwise we may miss some
> deadline.
>
> Tests using rt-app on Exynos5422 with up to 10 SCHED_DEADLINE tasks have
> shown reductions of even 10% of deadline misses with a negligible
> increase of energy consumption (measured through Baylibre Cape).
>
> Signed-off-by: Claudio Scordino <claudio@...dence.eu.com>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Patrick Bellasi <patrick.bellasi@....com>
> CC: Dietmar Eggemann <dietmar.eggemann@....com>
> CC: Morten Rasmussen <morten.rasmussen@....com>
> CC: Juri Lelli <juri.lelli@...hat.com>
> CC: Viresh Kumar <viresh.kumar@...aro.org>
> CC: Vincent Guittot <vincent.guittot@...aro.org>
> CC: Todd Kjos <tkjos@...roid.com>
> CC: Joel Fernandes <joelaf@...gle.com>
> CC: linux-pm@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> ---
> Changes from v2:
>  - Rate limit ignored also in case of "fast switch"
>  - Specific routine added
> ---
> Changes from v1:
>  - Logic moved from sugov_should_update_freq() to
>    sugov_update_single()/_shared() to not duplicate data structures
>  - Rate limit not ignored in case of "fast switch"
> ---
>  kernel/sched/cpufreq_schedutil.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 7936f54..13f9cce 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -260,6 +260,17 @@ static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu)
>  static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
>  #endif /* CONFIG_NO_HZ_COMMON */
>
> +/*
> + * Make sugov_should_update_freq() ignore the rate limit when DL
> + * has increased the utilization.
> + */
> +static inline

I wouldn't break the line here

> +void set_dl_rate_limit(struct sugov_cpu *sg_cpu, struct sugov_policy *sg_policy)

and the name might be better as Viresh said, but overall

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> +{
> +       if (cpu_util_dl(cpu_rq(sg_cpu->cpu)) > sg_cpu->util_dl)
> +               sg_policy->need_freq_update = true;
> +}
> +
>  static void sugov_update_single(struct update_util_data *hook, u64 time,
>                                 unsigned int flags)
>  {
> @@ -273,6 +284,8 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>         sugov_set_iowait_boost(sg_cpu, time);
>         sg_cpu->last_update = time;
>
> +       set_dl_rate_limit(sg_cpu, sg_policy);
> +
>         if (!sugov_should_update_freq(sg_policy, time))
>                 return;
>
> @@ -354,6 +367,8 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>
>         raw_spin_lock(&sg_policy->update_lock);
>
> +       set_dl_rate_limit(sg_cpu, sg_policy);
> +
>         sugov_get_util(sg_cpu);
>         sg_cpu->flags = flags;
>
> --
> 2.7.4
>