linux-kernel - Re: [PATCH] cpufreq: schedutil: Call sugov_update_next_freq() before check to fast_switch

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Date:   Wed, 24 Feb 2021 11:32:36 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Yue Hu <zbestahu@...il.com>
Cc:     rjw@...ysocki.net, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        huyue2@...ong.com, zbestahu@....com
Subject: Re: [PATCH] cpufreq: schedutil: Call sugov_update_next_freq() before
 check to fast_switch_enabled

On 24-02-21, 13:42, Yue Hu wrote:
> From: Yue Hu <huyue2@...ong.com>
> 
> Note that sugov_update_next_freq() may return false, that means the
> caller sugov_fast_switch() will do nothing except fast switch check.
> 
> Similarly, sugov_deferred_update() also has unnecessary operations
> of raw_spin_{lock,unlock} in sugov_update_single_freq() for that case.
> 
> So, let's call sugov_update_next_freq() before the fast switch check
> to avoid unnecessary behaviors above. Update the related interface
> definitions accordingly.
> 
> Signed-off-by: Yue Hu <huyue2@...ong.com>
> ---
>  kernel/sched/cpufreq_schedutil.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 41e498b..d23e5be 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -114,19 +114,13 @@ static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
>  	return true;
>  }
>  
> -static void sugov_fast_switch(struct sugov_policy *sg_policy, u64 time,
> -			      unsigned int next_freq)
> +static void sugov_fast_switch(struct sugov_policy *sg_policy, unsigned int next_freq)
>  {
> -	if (sugov_update_next_freq(sg_policy, time, next_freq))
> -		cpufreq_driver_fast_switch(sg_policy->policy, next_freq);
> +	cpufreq_driver_fast_switch(sg_policy->policy, next_freq);

I will call this directly instead, no need of the wrapper anymore.

>  }
>  
> -static void sugov_deferred_update(struct sugov_policy *sg_policy, u64 time,
> -				  unsigned int next_freq)
> +static void sugov_deferred_update(struct sugov_policy *sg_policy)
>  {
> -	if (!sugov_update_next_freq(sg_policy, time, next_freq))
> -		return;
> -
>  	if (!sg_policy->work_in_progress) {
>  		sg_policy->work_in_progress = true;
>  		irq_work_queue(&sg_policy->irq_work);
> @@ -368,16 +362,19 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time,
>  		sg_policy->cached_raw_freq = cached_freq;
>  	}
>  
> +	if (!sugov_update_next_freq(sg_policy, time, next_f))
> +		return;
> +
>  	/*
>  	 * This code runs under rq->lock for the target CPU, so it won't run
>  	 * concurrently on two different CPUs for the same target and it is not
>  	 * necessary to acquire the lock in the fast switch case.
>  	 */
>  	if (sg_policy->policy->fast_switch_enabled) {
> -		sugov_fast_switch(sg_policy, time, next_f);
> +		sugov_fast_switch(sg_policy, next_f);
>  	} else {
>  		raw_spin_lock(&sg_policy->update_lock);
> -		sugov_deferred_update(sg_policy, time, next_f);
> +		sugov_deferred_update(sg_policy);
>  		raw_spin_unlock(&sg_policy->update_lock);
>  	}
>  }
> @@ -456,12 +453,15 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
>  	if (sugov_should_update_freq(sg_policy, time)) {
>  		next_f = sugov_next_freq_shared(sg_cpu, time);
>  
> +		if (!sugov_update_next_freq(sg_policy, time, next_f))
> +			goto unlock;
> +
>  		if (sg_policy->policy->fast_switch_enabled)
> -			sugov_fast_switch(sg_policy, time, next_f);
> +			sugov_fast_switch(sg_policy, next_f);
>  		else
> -			sugov_deferred_update(sg_policy, time, next_f);
> +			sugov_deferred_update(sg_policy);
>  	}
> -
> +unlock:
>  	raw_spin_unlock(&sg_policy->update_lock);
>  }

-- 
viresh