linux-kernel - Re: [PATCH] cpufreq: Fix serialization of frequency transitions

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Date:	Tue, 02 Jul 2013 13:37:33 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, robin.randhawa@....com,
	Steve.Bannister@....com, Liviu.Dudau@....com,
	charles.garcia-tobin@....com, arvind.chauhan@....com,
	broonie@...aro.org
Subject: Re: [PATCH] cpufreq: Fix serialization of frequency transitions

On Tuesday, July 02, 2013 04:36:28 PM Viresh Kumar wrote:
> Commit 7c30ed ("cpufreq: make sure frequency transitions are serialized")
> interacts poorly with systems that have a single core freqency for all
> cores.  On such systems we have a single policy for all cores with
> several CPUs.  When we do a frequency transition the governor calls the
> pre and post change notifiers which causes cpufreq_notify_transition()
> per CPU.  Since the policy is the same for all of them all CPUs after
> the first and the warnings added are generated by checking a per-policy
> flag the warnings will be triggered for all cores after the first.
> 
> Fix this by allowing notifier to be called for n times. Where n is the number of
> cpus in policy->cpus.
> 
> Reported-and-Tested-by: Mark Brown <broonie@...aro.org>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> Hi Rafael,
> 
> This is a fix for 3.11.

Queued up for 3.11.

Thanks,
Rafael


>  drivers/cpufreq/cpufreq.c | 7 ++++---
>  include/linux/cpufreq.h   | 2 +-
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index b557503..b7bda8d 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -312,11 +312,12 @@ static void __cpufreq_notify_transition(struct cpufreq_policy *policy,
>  	switch (state) {
>  
>  	case CPUFREQ_PRECHANGE:
> -		if (WARN(policy->transition_ongoing,
> +		if (WARN(policy->transition_ongoing ==
> +					cpumask_weight(policy->cpus),
>  				"In middle of another frequency transition\n"))
>  			return;
>  
> -		policy->transition_ongoing = true;
> +		policy->transition_ongoing++;
>  
>  		/* detect if the driver reported a value as "old frequency"
>  		 * which is not equal to what the cpufreq core thinks is
> @@ -341,7 +342,7 @@ static void __cpufreq_notify_transition(struct cpufreq_policy *policy,
>  				"No frequency transition in progress\n"))
>  			return;
>  
> -		policy->transition_ongoing = false;
> +		policy->transition_ongoing--;
>  
>  		adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
>  		pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 4d7390b..90d5a15 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -119,7 +119,7 @@ struct cpufreq_policy {
>  
>  	struct kobject		kobj;
>  	struct completion	kobj_unregister;
> -	bool			transition_ongoing; /* Tracks transition status */
> +	int			transition_ongoing; /* Tracks transition status */
>  };
>  
>  #define CPUFREQ_ADJUST			(0)
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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