linux-kernel - Re: [PATCH v6 2/4] scmi-cpufreq: Move CPU initialisation to probe

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Message-ID: <20210112111717.5ds446w2kroxzvhr@vireshk-i7>
Date:   Tue, 12 Jan 2021 16:47:17 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Nicola Mazzucato <nicola.mazzucato@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, sudeep.holla@....com, rjw@...ysocki.net,
        vireshk@...nel.org, cristian.marussi@....com,
        morten.rasmussen@....com, chris.redpath@....com
Subject: Re: [PATCH v6 2/4] scmi-cpufreq: Move CPU initialisation to probe

On 11-01-21, 15:45, Nicola Mazzucato wrote:
> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
> +static int scmi_init_cpudata(void)
> +{
> +	int cpu;
> +	unsigned int ncpus = num_possible_cpus();
> +
> +	cpudata_table = kzalloc(sizeof(*cpudata_table) * ncpus, GFP_KERNEL);
> +	if (!cpudata_table)
> +		return -ENOMEM;

This could have been done with a per-cpu variable instead.

> +	for_each_possible_cpu(cpu) {
> +		if (!zalloc_cpumask_var(&cpudata_table[cpu].scmi_shared_cpus,
> +					GFP_KERNEL))
> +			goto out;
> +	}

You are making a copy of the struct for each CPU and so for a 16 CPUs
sharing their clock lines, you will have 16 copies of the exact same
stuff.

An optimal approach would be to have a linked-list of this structure
and that will only have 1 node per cpufreq policy.

> +	return 0;
> +
> +out:
> +	kfree(cpudata_table);
> +	return -ENOMEM;
> +}
> +
> +static int scmi_init_device(const struct scmi_handle *handle, int cpu)
> +{
> +	struct device *cpu_dev;
> +	int ret, nr_opp;
> +	struct em_data_callback em_cb = EM_DATA_CB(scmi_get_cpu_power);
> +	bool power_scale_mw;
> +	cpumask_var_t scmi_cpus;
> +
> +	if (!zalloc_cpumask_var(&scmi_cpus, GFP_KERNEL))
> +		return -ENOMEM;
> +
> +	cpumask_set_cpu(cpu, scmi_cpus);
> +
> +	cpu_dev = get_cpu_device(cpu);
> +
> +	ret = scmi_get_sharing_cpus(cpu_dev, scmi_cpus);

Where do you expect the sharing information to come from in this case
? DT ?

> +	if (ret) {
> +		dev_warn(cpu_dev, "failed to get sharing cpumask\n");
> +		goto free_cpumask;
> +	}
> +
> +	/*
> +	 * We get here for each CPU. Add OPPs only on those CPUs for which we
> +	 * haven't already done so, or set their OPPs as shared.
> +	 */
> +	nr_opp = dev_pm_opp_get_opp_count(cpu_dev);
> +	if (nr_opp <= 0) {
> +		ret = handle->perf_ops->device_opps_add(handle, cpu_dev);
> +		if (ret) {
> +			dev_warn(cpu_dev, "failed to add opps to the device\n");
> +			goto free_cpumask;
> +		}
> +
> +		ret = dev_pm_opp_set_sharing_cpus(cpu_dev, scmi_cpus);
> +		if (ret) {
> +			dev_err(cpu_dev, "%s: failed to mark OPPs as shared: %d\n",
> +				__func__, ret);
> +			goto free_cpumask;
> +		}
> +
> +		nr_opp = dev_pm_opp_get_opp_count(cpu_dev);

Shouldn't you do this just after adding the OPPs ?

> +		if (nr_opp <= 0) {
> +			dev_err(cpu_dev, "%s: No OPPs for this device: %d\n",
> +				__func__, ret);
> +
> +			ret = -ENODEV;
> +			goto free_cpumask;
> +		}
> +
> +		power_scale_mw = handle->perf_ops->power_scale_mw_get(handle);
> +		em_dev_register_perf_domain(cpu_dev, nr_opp, &em_cb, scmi_cpus,
> +					    power_scale_mw);
> +	}
> +
> +	ret = dev_pm_opp_init_cpufreq_table(cpu_dev,
> +					    &cpudata_table[cpu].freq_table);
> +	if (ret) {
> +		dev_err(cpu_dev, "failed to init cpufreq table: %d\n", ret);
> +		goto free_cpumask;
> +	}
> +
> +	cpumask_copy(cpudata_table[cpu].scmi_shared_cpus, scmi_cpus);
> +
> +free_cpumask:
> +	free_cpumask_var(scmi_cpus);
> +	return ret;
> +}
> +
>  static int scmi_cpufreq_probe(struct scmi_device *sdev)
>  {
>  	int ret;
>  	struct device *dev = &sdev->dev;
> +	int cpu;
> +	struct device *cpu_dev;

Please keep the list of local variable in decreasing order of their
length, many people including me prefer it that way.

>  
>  	handle = sdev->handle;
>  
> @@ -247,6 +305,24 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
>  		devm_of_clk_add_hw_provider(dev, of_clk_hw_simple_get, NULL);
>  #endif
>  
> +	ret = scmi_init_cpudata();
> +	if (ret) {
> +		pr_err("%s: init cpu data failed\n", __func__);
> +		return ret;
> +	}
> +
> +	for_each_possible_cpu(cpu) {
> +		cpu_dev = get_cpu_device(cpu);
> +
> +		ret = scmi_init_device(handle, cpu);
> +		if (ret) {
> +			dev_err(cpu_dev, "%s: init device failed\n",
> +				__func__);
> +
> +			return ret;

You missed undoing scmi_init_cpudata().

> +		}
> +	}
> +
>  	ret = cpufreq_register_driver(&scmi_cpufreq_driver);
>  	if (ret) {
>  		dev_err(dev, "%s: registering cpufreq failed, err: %d\n",
> @@ -258,6 +334,20 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
>  
>  static void scmi_cpufreq_remove(struct scmi_device *sdev)
>  {
> +	int cpu;
> +	struct device *cpu_dev;
> +
> +	for_each_possible_cpu(cpu) {
> +		cpu_dev = get_cpu_device(cpu);
> +
> +		dev_pm_opp_free_cpufreq_table(cpu_dev,
> +					      &cpudata_table[cpu].freq_table);
> +
> +		free_cpumask_var(cpudata_table[cpu].scmi_shared_cpus);
> +	}
> +
> +	kfree(cpudata_table);
> +
>  	cpufreq_unregister_driver(&scmi_cpufreq_driver);
>  }
>  
> -- 
> 2.27.0

-- 
viresh