linux-kernel - Re: [PATCH 2/2] cpufreq: don't call cpufreq_update

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Date:	Mon, 17 Feb 2014 14:13:26 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	rjw@...ysocki.net, linaro-kernel@...ts.linaro.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, pierre-list@...man.eu
Subject: Re: [PATCH 2/2] cpufreq: don't call cpufreq_update_policy() on CPU
 addition

On 02/14/2014 04:30 PM, Viresh Kumar wrote:
> cpufreq_update_policy() is called from two places currently. From a workqueue
> handled queued from cpufreq_bp_resume() for boot CPU and from
> cpufreq_cpu_callback() whenever a CPU is added.
> 
> The first one makes sure that boot CPU is running on the frequency present in
> policy->cpu. But we don't really need a call from cpufreq_cpu_callback(),
> because we always call cpufreq_driver->init() (which will set policy->cur
> correctly) whenever first CPU of any policy is added back. And so every policy
> structure is guaranteed to have the right frequency in policy->cur.
>

This wording is slightly inaccurate. ->init() may or may not set policy->cur
(for example, powernowk8 driver doesn't set it in the init routine)..
But we set it for sure in __cpufreq_add_dev():

1117         if (cpufreq_driver->get) {
1118                 policy->cur = cpufreq_driver->get(policy->cpu);
1119                 if (!policy->cur) {
1120                         pr_err("%s: ->get() failed\n", __func__);
1121                         goto err_get_freq;
1122                 }
1123         }

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

The reasoning and the code looks good to me.

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Regards,
Srivatsa S. Bhat

> ---
>  drivers/cpufreq/cpufreq.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 383362b..b6eb4ed 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2194,7 +2194,6 @@ static int cpufreq_cpu_callback(struct notifier_block *nfb,
>  		switch (action & ~CPU_TASKS_FROZEN) {
>  		case CPU_ONLINE:
>  			__cpufreq_add_dev(dev, NULL, frozen);
> -			cpufreq_update_policy(cpu);
>  			break;
> 
>  		case CPU_DOWN_PREPARE:
> 

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