[PATCH] cpufreq: Fix serialization of frequency transitions

[PATCH] cpufreq: Fix serialization of frequency transitions

[Viresh Kumar]

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@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
Hi Rafael,

This is a fix for 3.11.

 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)
-- 
1.7.12.rc2.18.g61b472e

Re: [PATCH] cpufreq: Fix serialization of frequency transitions

[Rafael J. Wysocki]

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