linux-kernel - Re: [PATCH RFC] schedutil: Allow cpufreq requests to be made even when kthread kicked

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Message-ID: <20180517050611.yj2alkzckl3ximzu@vireshk-i7>
Date:   Thu, 17 May 2018 10:36:11 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Joel Fernandes <joelaf@...gle.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH RFC] schedutil: Allow cpufreq requests to be made even
 when kthread kicked

On 16-05-18, 15:45, Joel Fernandes (Google) wrote:
>  kernel/sched/cpufreq_schedutil.c | 36 +++++++++++++++++++++++++-------
>  1 file changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index e13df951aca7..a87fc281893d 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -92,9 +92,6 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
>  	    !cpufreq_can_do_remote_dvfs(sg_policy->policy))
>  		return false;
>  
> -	if (sg_policy->work_in_progress)
> -		return false;
> -
>  	if (unlikely(sg_policy->need_freq_update)) {
>  		sg_policy->need_freq_update = false;
>  		/*
> @@ -129,8 +126,11 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
>  		policy->cur = next_freq;
>  		trace_cpu_frequency(next_freq, smp_processor_id());
>  	} else {
> -		sg_policy->work_in_progress = true;
> -		irq_work_queue(&sg_policy->irq_work);
> +		/* Don't queue request if one was already queued */
> +		if (!sg_policy->work_in_progress) {

Merge it above to make it "else if".

> +			sg_policy->work_in_progress = true;
> +			irq_work_queue(&sg_policy->irq_work);
> +		}
>  	}
>  }
>  
> @@ -291,6 +291,15 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>  
>  	ignore_dl_rate_limit(sg_cpu, sg_policy);
>  
> +	/*
> +	 * For slow-switch systems, single policy requests can't run at the
> +	 * moment if the governor thread is already processing a pending
> +	 * frequency switch request, this can be fixed by acquiring update_lock
> +	 * while updating next_freq and work_in_progress but we prefer not to.
> +	 */
> +	if (sg_policy->work_in_progress)
> +		return;
> +

@Rafael: Do you think its worth start using the lock now for unshared
policies ?

>  	if (!sugov_should_update_freq(sg_policy, time))
>  		return;
>  
> @@ -382,13 +391,24 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags)
>  static void sugov_work(struct kthread_work *work)
>  {
>  	struct sugov_policy *sg_policy = container_of(work, struct sugov_policy, work);
> +	unsigned int freq;
> +	unsigned long flags;
> +
> +	/*
> +	 * Hold sg_policy->update_lock shortly to handle the case where:
> +	 * incase sg_policy->next_freq is read here, and then updated by
> +	 * sugov_update_shared just before work_in_progress is set to false
> +	 * here, we may miss queueing the new update.
> +	 */
> +	raw_spin_lock_irqsave(&sg_policy->update_lock, flags);
> +	freq = sg_policy->next_freq;
> +	sg_policy->work_in_progress = false;
> +	raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags);
>  
>  	mutex_lock(&sg_policy->work_lock);
> -	__cpufreq_driver_target(sg_policy->policy, sg_policy->next_freq,
> +	__cpufreq_driver_target(sg_policy->policy, freq,
>  				CPUFREQ_RELATION_L);

No need of line break anymore.

>  	mutex_unlock(&sg_policy->work_lock);
> -
> -	sg_policy->work_in_progress = false;
>  }
>  
>  static void sugov_irq_work(struct irq_work *irq_work)

LGTM.

-- 
viresh