linux-kernel - Re: [RFC PATCH v2 1/8] sched/cpufreq_schedutil: make use of DEADLINE utilization signal

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Date:   Tue, 5 Dec 2017 15:09:35 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     peterz@...radead.org, mingo@...hat.com, rjw@...ysocki.net,
        viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, tglx@...utronix.de,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        luca.abeni@...tannapisa.it, claudio@...dence.eu.com,
        tommaso.cucinotta@...tannapisa.it, bristot@...hat.com,
        mathieu.poirier@...aro.org, tkjos@...roid.com, joelaf@...gle.com,
        morten.rasmussen@....com, dietmar.eggemann@....com,
        alessio.balsini@....com, Juri Lelli <juri.lelli@....com>,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH v2 1/8] sched/cpufreq_schedutil: make use of DEADLINE
 utilization signal

Hi Juri,

On 04-Dec 11:23, Juri Lelli wrote:
> From: Juri Lelli <juri.lelli@....com>
> 
> SCHED_DEADLINE tracks active utilization signal with a per dl_rq
> variable named running_bw.
> 
> Make use of that to drive cpu frequency selection: add up FAIR and
> DEADLINE contribution to get the required CPU capacity to handle both
> requirements (while RT still selects max frequency).
> 
> Co-authored-by: Claudio Scordino <claudio@...dence.eu.com>
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Luca Abeni <luca.abeni@...tannapisa.it>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  include/linux/sched/cpufreq.h    |  2 --
>  kernel/sched/cpufreq_schedutil.c | 25 +++++++++++++++----------
>  2 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
> index d1ad3d825561..0b55834efd46 100644
> --- a/include/linux/sched/cpufreq.h
> +++ b/include/linux/sched/cpufreq.h
> @@ -12,8 +12,6 @@
>  #define SCHED_CPUFREQ_DL	(1U << 1)
>  #define SCHED_CPUFREQ_IOWAIT	(1U << 2)
>  
> -#define SCHED_CPUFREQ_RT_DL	(SCHED_CPUFREQ_RT | SCHED_CPUFREQ_DL)
> -
>  #ifdef CONFIG_CPU_FREQ
>  struct update_util_data {
>         void (*func)(struct update_util_data *data, u64 time, unsigned int flags);
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 2f52ec0f1539..de1ad1fffbdc 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -179,12 +179,17 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>  static void sugov_get_util(unsigned long *util, unsigned long *max, int cpu)
>  {
>  	struct rq *rq = cpu_rq(cpu);
> -	unsigned long cfs_max;
> +	unsigned long dl_util = (rq->dl.running_bw * SCHED_CAPACITY_SCALE)
> +				>> BW_SHIFT;

What about using a pair of getter methods (e.g. cpu_util_{cfs,dl}) to
be defined in kernel/sched/sched.h?

This would help to hide class-specific signals mangling from cpufreq.
And here we can have something "more abstract" like:

       unsigned long util_cfs = cpu_util_cfs(rq);
       unsigned long util_dl = cpu_util_dl(rq);

>  
> -	cfs_max = arch_scale_cpu_capacity(NULL, cpu);
> +	*max = arch_scale_cpu_capacity(NULL, cpu);
>  
> -	*util = min(rq->cfs.avg.util_avg, cfs_max);
> -	*max = cfs_max;
> +	/*
> +	 * Ideally we would like to set util_dl as min/guaranteed freq and
> +	 * util_cfs + util_dl as requested freq. However, cpufreq is not yet
> +	 * ready for such an interface. So, we only do the latter for now.
> +	 */

Maybe I don't completely get the above comment, but to me it is not
really required.

When you say that "util_dl" should be set to a min/guaranteed freq
are you not actually talking about a DL implementation detail?

>From the cpufreq standpoint instead, we should always set a capacity
which can accommodate util_dl + util_cfs.

We don't care about the meaning of util_dl and we should always assume
(by default) that the signal is properly updated by the scheduling
class... which unfortunately does not always happen for CFS.


> +	*util = min(rq->cfs.avg.util_avg + dl_util, *max);

With the above proposal, here also we will have:

	*util = min(util_cfs + util_dl, *max);

>  }
>  
>  static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> @@ -272,7 +277,7 @@ 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) {
> +	if (flags & SCHED_CPUFREQ_RT) {
>  		next_f = policy->cpuinfo.max_freq;
>  	} else {
>  		sugov_get_util(&util, &max, sg_cpu->cpu);
> @@ -317,7 +322,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
>  			j_sg_cpu->iowait_boost_pending = false;
>  			continue;
>  		}
> -		if (j_sg_cpu->flags & SCHED_CPUFREQ_RT_DL)
> +		if (j_sg_cpu->flags & SCHED_CPUFREQ_RT)
>  			return policy->cpuinfo.max_freq;
>  
>  		j_util = j_sg_cpu->util;
> @@ -353,7 +358,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>  	sg_cpu->last_update = time;
>  
>  	if (sugov_should_update_freq(sg_policy, time)) {
> -		if (flags & SCHED_CPUFREQ_RT_DL)
> +		if (flags & SCHED_CPUFREQ_RT)
>  			next_f = sg_policy->policy->cpuinfo.max_freq;
>  		else
>  			next_f = sugov_next_freq_shared(sg_cpu, time);
> @@ -383,9 +388,9 @@ static void sugov_irq_work(struct irq_work *irq_work)
>  	sg_policy = container_of(irq_work, struct sugov_policy, irq_work);
>  
>  	/*
> -	 * For RT and deadline tasks, the schedutil governor shoots the
> -	 * frequency to maximum. Special care must be taken to ensure that this
> -	 * kthread doesn't result in the same behavior.
> +	 * For RT tasks, the schedutil governor shoots the frequency to maximum.
> +	 * Special care must be taken to ensure that this kthread doesn't result
> +	 * in the same behavior.
>  	 *
>  	 * This is (mostly) guaranteed by the work_in_progress flag. The flag is
>  	 * updated only at the end of the sugov_work() function and before that
> -- 
> 2.14.3
> 

-- 
#include <best/regards.h>

Patrick Bellasi