linux-kernel - Re: [PATCH v3 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver

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Message-ID: <939f7943-feec-aaa2-3bd3-59a6618330c0@linaro.org>
Date:   Fri, 13 Apr 2018 13:47:50 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     viresh.kumar@...aro.org, edubezval@...il.com,
        kevin.wangtao@...aro.org, leo.yan@...aro.org,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        javi.merino@...nel.org, rui.zhang@...el.com,
        daniel.thompson@...aro.org, linux-pm@...r.kernel.org,
        Amit Daniel Kachhap <amit.kachhap@...il.com>
Subject: Re: [PATCH v3 6/7] thermal/drivers/cpu_cooling: Introduce the cpu
 idle cooling driver

On 13/04/2018 13:23, Sudeep Holla wrote:
> Hi Daniel,
> 
> On 05/04/18 17:16, Daniel Lezcano wrote:
> 
> [...]
> 
>> +/**
>> + * cpuidle_cooling_register - Idle cooling device initialization function
>> + *
>> + * This function is in charge of creating a cooling device per cluster
>> + * and register it to thermal framework. For this we rely on the
>> + * topology as there is nothing yet describing better the idle state
>> + * power domains.
>> + *
>> + * We create a cpuidle cooling device per cluster. For this reason we
>> + * must, for each cluster, allocate and initialize the cooling device
>> + * and for each cpu belonging to this cluster, do the initialization
>> + * on a cpu basis.
>> + *
>> + * This approach for creating the cooling device is needed as we don't
>> + * have the guarantee the CPU numbering is sequential.
>> + *
>> + * Unfortunately, there is no API to browse from top to bottom the
>> + * topology, cluster->cpu, only the usual for_each_possible_cpu loop.
>> + * In order to solve that, we use a cpumask to flag the cluster_id we
>> + * already processed. The cpumask will always have enough room for all
>> + * the cluster because it is based on NR_CPUS and it is not possible
>> + * to have more clusters than cpus.
>> + *
>> + */
>> +void __init cpuidle_cooling_register(void)
>> +{
>> +	struct cpuidle_cooling_device *idle_cdev = NULL;
>> +	struct thermal_cooling_device *cdev;
>> +	struct device_node *np;
>> +	cpumask_var_t cpumask;
>> +	char dev_name[THERMAL_NAME_LENGTH];
>> +	int ret = -ENOMEM, cpu;
>> +	int cluster_id;
>> +
>> +	if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
>> +		return;
>> +
>> +	for_each_possible_cpu(cpu) {
>> +
>> +		cluster_id = topology_physical_package_id(cpu);
>> +		if (cpumask_test_cpu(cluster_id, cpumask))
>> +			continue;
> 
> Sorry for chiming in randomly, I haven't read the patches in detail.
> But it was brought to my notice that topology_physical_package_id is
> being used for cluster ID here. It's completely wrong and will
> changesoon with ACPI topology related changes Jeremy is working on.
> 
> You will get the physical socket number(which is mostly 0 on single SoC
> system). Makes sure that this won't break with that change.
> 
> Please note with cluster id not defined architecturally, relying on that
> is simply problematic.

Ok, noted. At the first glance, it should not be a problem.


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