linux-kernel - Re: [RFC PATCH v3 2/6] sched/cpufreq: Attach perf domain to sugov policy

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Message-ID: <686407a7-3074-0fa2-e041-a9931f467aea@arm.com>
Date:   Thu, 17 Oct 2019 11:22:16 +0100
From:   Douglas Raillard <douglas.raillard@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org
Cc:     linux-pm@...r.kernel.org, mingo@...hat.com, peterz@...radead.org,
        rjw@...ysocki.net, viresh.kumar@...aro.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, qperret@...rret.net,
        patrick.bellasi@...bug.net, dh.han@...sung.com
Subject: Re: [RFC PATCH v3 2/6] sched/cpufreq: Attach perf domain to sugov
 policy

Hi Dietmar,

On 10/17/19 9:57 AM, Dietmar Eggemann wrote:
> On 11/10/2019 15:44, Douglas RAILLARD wrote:
> 
> [...]
> 
>> @@ -66,6 +70,38 @@ static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu);
>>   
>>   /************************ Governor internals ***********************/
>>   
>> +#ifdef CONFIG_ENERGY_MODEL
>> +static void sugov_policy_attach_pd(struct sugov_policy *sg_policy)
>> +{
>> +	struct em_perf_domain *pd;
>> +	struct cpufreq_policy *policy = sg_policy->policy;
> 
> Shouldn't always order local variable declarations from longest to
> shortest line?

Can't find any reference to that rule in the coding style, although I'm happy to change order
if that's deemed useful.

> 
>> +
>> +	sg_policy->pd = NULL;
>> +	pd = em_cpu_get(policy->cpu);
>> +	if (!pd)
>> +		return;
>> +
>> +	if (cpumask_equal(policy->related_cpus, to_cpumask(pd->cpus)))
>> +		sg_policy->pd = pd;
>> +	else
>> +		pr_warn("%s: Not all CPUs in schedutil policy %u share the same perf domain, no perf domain for that policy will be registered\n",
>> +			__func__, policy->cpu);
> 
> Maybe {} because of 2 lines?

+1

>> +}
>> +
>> +static struct em_perf_domain *sugov_policy_get_pd(
>> +						struct sugov_policy *sg_policy)
> 
> 
> Maybe this way? This format is already used in this file.
> 
> static struct em_perf_domain *
> sugov_policy_get_pd(struct sugov_policy *sg_policy)
> 

I also prefer this kind of non-indented form that always stays indented across renames :)

>> +{
>> +	return sg_policy->pd;
>> +}
>> +#else /* CONFIG_ENERGY_MODEL */
>> +static void sugov_policy_attach_pd(struct sugov_policy *sg_policy) {}
>> +static struct em_perf_domain *sugov_policy_get_pd(
>> +						struct sugov_policy *sg_policy)
>> +{
>> +	return NULL;
>> +}
>> +#endif /* CONFIG_ENERGY_MODEL */
>> +
>>   static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
>>   {
>>   	s64 delta_ns;
>> @@ -859,6 +895,9 @@ static int sugov_start(struct cpufreq_policy *policy)
>>   							sugov_update_shared :
>>   							sugov_update_single);
>>   	}
>> +
>> +	sugov_policy_attach_pd(sg_policy);
>> +
>>   	return 0;
>>   }
> 
> A sugov_policy_detach_pd() called from sugov_stop() (doing for instance
> the g_policy->pd = NULL) is not needed?

 From what I could see, sugov_stop() will always be followed by sugov_start() before
it's used again, so that does not seem more risky than not de-initializing sg_cpu's
for example.