linux-kernel - Re: [PATCH 7/12] cpufreq: ondemand: Rework the handling of powersave bias updates

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Message-ID: <20160218055354.GM2610@vireshk-i7>
Date:	Thu, 18 Feb 2016 11:23:54 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/12] cpufreq: ondemand: Rework the handling of powersave
 bias updates

On 18-02-16, 02:28, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The ondemand_powersave_bias_init() function used for resetting data
> fields related to the powersave bias tunable of the ondemand governor
> works by walking all of the online CPUs in the system and updating the
> od_cpu_dbs_info_s structures for all of them.
> 
> However, if governor tunables are per policy, the update should not
> touch the CPUs that are not associated with the given dbs_data.
> 
> Moreover, since the data fields in question are only ever used for
> policy->cpu in each policy governed by ondemand, the update can be
> limited to those specific CPUs.

Now that I am looking at struct **_cpu_dbs_info_s definitions, I think
we need to change the design of the structures a bit. Only cdbs is
something that is per-cpu and everything else is per-policy. And so we
will be able to move the per-cpu structures present in individual
governors into cpufreq_governor.c and save some memory.

> Rework the code to take the above observations into account.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpufreq/cpufreq_ondemand.c |   30 +++++++++++++-----------------
>  1 file changed, 13 insertions(+), 17 deletions(-)
> 
> Index: linux-pm/drivers/cpufreq/cpufreq_ondemand.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq_ondemand.c
> +++ linux-pm/drivers/cpufreq/cpufreq_ondemand.c
> @@ -34,14 +34,6 @@ static struct od_ops od_ops;
>  
>  static unsigned int default_powersave_bias;
>  
> -static void ondemand_powersave_bias_init_cpu(int cpu)
> -{
> -	struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
> -
> -	dbs_info->freq_table = cpufreq_frequency_get_table(cpu);
> -	dbs_info->freq_lo = 0;
> -}
> -
>  /*
>   * Not all CPUs want IO time to be accounted as busy; this depends on how
>   * efficient idling at a higher frequency/voltage is.
> @@ -120,12 +112,13 @@ static unsigned int generic_powersave_bi
>  	return freq_hi;
>  }
>  
> -static void ondemand_powersave_bias_init(void)
> +static void ondemand_powersave_bias_init(struct cpufreq_policy *policy)
>  {
> -	int i;
> -	for_each_online_cpu(i) {
> -		ondemand_powersave_bias_init_cpu(i);
> -	}
> +	unsigned int cpu = policy->cpu;
> +	struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
> +
> +	dbs_info->freq_table = cpufreq_frequency_get_table(cpu);
> +	dbs_info->freq_lo = 0;
>  }
>  
>  static void dbs_freq_increase(struct cpufreq_policy *policy, unsigned int freq)
> @@ -306,6 +299,7 @@ static ssize_t store_powersave_bias(stru
>  		size_t count)
>  {
>  	struct od_dbs_tuners *od_tuners = dbs_data->tuners;
> +	struct policy_dbs_info *policy_dbs;
>  	unsigned int input;
>  	int ret;
>  	ret = sscanf(buf, "%u", &input);
> @@ -317,7 +311,10 @@ static ssize_t store_powersave_bias(stru
>  		input = 1000;
>  
>  	od_tuners->powersave_bias = input;
> -	ondemand_powersave_bias_init();
> +
> +	list_for_each_entry(policy_dbs, &dbs_data->policy_dbs_list, list)
> +		ondemand_powersave_bias_init(policy_dbs->policy);
> +
>  	return count;
>  }
>  
> @@ -398,11 +395,10 @@ static void od_exit(struct dbs_data *dbs
>  
>  static void od_start(struct cpufreq_policy *policy)
>  {
> -	unsigned int cpu = policy->cpu;
> -	struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
> +	struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, policy->cpu);
>  
>  	dbs_info->sample_type = OD_NORMAL_SAMPLE;
> -	ondemand_powersave_bias_init_cpu(cpu);
> +	ondemand_powersave_bias_init(policy);
>  }
>  
>  define_get_cpu_dbs_routines(od_cpu_dbs_info);

I agree with the patch, but because we have all these fields per-cpu,
I feel a bit scared while depending on policy->cpu for everything.

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh