linux-kernel - Re: [PATCH] cpufreq: schedutil: Update cached "current frequency" when limits change

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Message-ID: <20170712052448.GI17115@vireshk-i7>
Date:   Wed, 12 Jul 2017 10:54:48 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Saravana Kannan <skannan@...eaurora.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: schedutil: Update cached "current frequency"
 when limits change

On 11-07-17, 19:24, Saravana Kannan wrote:
> Currently, the governor calculates the next frequency, set the current CPU
> frequency (policy->cur). It also assumes the current CPU frequency doesn't
> change if the next frequency isn't calculated again and hence caches the
> "current frequency".
> 
> However, this isn't true when CPU min/max frequency limits are changed. So,
> there's room for the CPU frequency to get stuck at the wrong level if the
> calculated next frequency doesn't change across multiple limits updates.
> 
> Fix this by updating the cached "current frequency" when limits changes the
> current CPU frequency.
> 
> Signed-off-by: Saravana Kannan <skannan@...eaurora.org>
> ---
>  kernel/sched/cpufreq_schedutil.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 076a2e3..fe0b2fb 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -226,6 +226,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>  
>  	busy = sugov_cpu_is_busy(sg_cpu);
>  
> +	raw_spin_lock(&sg_policy->update_lock);
>  	if (flags & SCHED_CPUFREQ_RT_DL) {
>  		next_f = policy->cpuinfo.max_freq;
>  	} else {
> @@ -240,6 +241,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>  			next_f = sg_policy->next_freq;
>  	}
>  	sugov_update_commit(sg_policy, time, next_f);
> +	raw_spin_unlock(&sg_policy->update_lock);

We wouldn't allow locking here until the time we can :)

>  }
>  
>  static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
> @@ -637,10 +639,14 @@ static void sugov_stop(struct cpufreq_policy *policy)
>  static void sugov_limits(struct cpufreq_policy *policy)
>  {
>  	struct sugov_policy *sg_policy = policy->governor_data;
> +	unsigned long flags;
>  
>  	if (!policy->fast_switch_enabled) {
>  		mutex_lock(&sg_policy->work_lock);
>  		cpufreq_policy_apply_limits(policy);
> +		raw_spin_lock_irqsave(&sg_policy->update_lock, flags);
> +		sg_policy->next_freq = policy->cur;
> +		raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags);
>  		mutex_unlock(&sg_policy->work_lock);
>  	}

Did you miss the following part which is after the closing } here ?

        sg_policy->need_freq_update = true;

As this should already take care of the problem you are worried about. Or did I
misunderstood your problem completely ?

-- 
viresh