linux-kernel - Re: [PATCH v2 3/6] cpufreq: schedutil: ensure max frequency while running RT/DL tasks

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Date:   Wed, 5 Jul 2017 11:31:36 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@....com>,
        Joel Fernandes <joelaf@...gle.com>,
        Andres Oportus <andresoportus@...gle.com>,
        Todd Kjos <tkjos@...roid.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steve Muckle <smuckle.linux@...il.com>
Subject: Re: [PATCH v2 3/6] cpufreq: schedutil: ensure max frequency while
 running RT/DL tasks

On 04-07-17, 18:34, Patrick Bellasi wrote:
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 004ae18..98704d8 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -216,6 +216,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>  	struct cpufreq_policy *policy = sg_policy->policy;
>  	unsigned long util, max;
>  	unsigned int next_f;
> +	bool rt_mode;
>  	bool busy;
>  
>  	/* Skip updates generated by sugov kthreads */
> @@ -230,7 +231,15 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>  
>  	busy = sugov_cpu_is_busy(sg_cpu);
>  
> -	if (flags & SCHED_CPUFREQ_RT_DL) {
> +	/*
> +	 * While RT/DL tasks are running we do not want FAIR tasks to
> +	 * overvrite this CPU's flags, still we can update utilization and
> +	 * frequency (if required/possible) to be fair with these tasks.
> +	 */
> +	rt_mode = task_has_dl_policy(current) ||
> +		  task_has_rt_policy(current) ||
> +		  (flags & SCHED_CPUFREQ_RT_DL);

We may want to create a separate inline function for above, as it is already
used twice in this patch.

But I was wondering if we can get some help from the scheduler to avoid such
code here. I understand that we don't want to do the aggregation in the
scheduler to keep it clean and keep such governor specific thing here.

But what about clearing the sched-class's flag from .pick_next_task() callback
when they return NULL ?

What about something like this instead (completely untested), with which we
don't need the 2/3 patch as well:

diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
index d2be2ccbb372..e81a6b5591f5 100644
--- a/include/linux/sched/cpufreq.h
+++ b/include/linux/sched/cpufreq.h
@@ -11,6 +11,10 @@
 #define SCHED_CPUFREQ_DL       (1U << 1)
 #define SCHED_CPUFREQ_IOWAIT   (1U << 2)
 
+#define SCHED_CPUFREQ_CLEAR    (1U << 31)
+#define SCHED_CPUFREQ_CLEAR_RT (SCHED_CPUFREQ_CLEAR | SCHED_CPUFREQ_RT)
+#define SCHED_CPUFREQ_CLEAR_DL (SCHED_CPUFREQ_CLEAR | SCHED_CPUFREQ_DL)
+
 #define SCHED_CPUFREQ_RT_DL    (SCHED_CPUFREQ_RT | SCHED_CPUFREQ_DL)
 
 #ifdef CONFIG_CPU_FREQ
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 076a2e31951c..f32e15d59d62 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -218,6 +218,9 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
        unsigned int next_f;
        bool busy;
 
+       if (flags & SCHED_CPUFREQ_CLEAR)
+               return;
+
        sugov_set_iowait_boost(sg_cpu, time, flags);
        sg_cpu->last_update = time;
 
@@ -296,7 +299,13 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
 
        sg_cpu->util = util;
        sg_cpu->max = max;
-       sg_cpu->flags = flags;
+
+       if (unlikely(flags & SCHED_CPUFREQ_CLEAR)) {
+               sg_cpu->flags &= ~(flags & ~SCHED_CPUFREQ_CLEAR);
+               return;
+       }
+
+       sg_cpu->flags |= flags;
 
        sugov_set_iowait_boost(sg_cpu, time, flags);
        sg_cpu->last_update = time;
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a2ce59015642..441d6153d654 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1203,8 +1203,10 @@ pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
        if (prev->sched_class == &dl_sched_class)
                update_curr_dl(rq);
 
-       if (unlikely(!dl_rq->dl_nr_running))
+       if (unlikely(!dl_rq->dl_nr_running)) {
+               cpufreq_update_this_cpu(rq, SCHED_CPUFREQ_CLEAR_DL);
                return NULL;
+       }
 
        put_prev_task(rq, prev);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 979b7341008a..bca9e4bb7ec4 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1556,8 +1556,10 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
        if (prev->sched_class == &rt_sched_class)
                update_curr_rt(rq);
 
-       if (!rt_rq->rt_queued)
+       if (!rt_rq->rt_queued) {
+               cpufreq_update_this_cpu(rq, SCHED_CPUFREQ_CLEAR_RT);
                return NULL;
+       }
 
        put_prev_task(rq, prev);

-- 
viresh