linux-kernel - Re: [PATCH 2.6.25.10] pm_qos_params: change spinlock to rwlock

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Date:	Wed, 16 Jul 2008 10:15:47 -0700
From:	mark gross <mgross@...ux.intel.com>
To:	"Jakub W. Jozwicki" <jozwicki@...er.pl>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.25.10] pm_qos_params: change spinlock to rwlock

nack.


On Sun, Jul 13, 2008 at 01:19:19AM +0200, Jakub W. Jozwicki wrote:
> Concurrent calls to pm_qos_requirement shouldn't block each other. This patch 
> changes spinlock to rwlock and fixes issues with PREEMPT_RT.
>  
> Signed-off-by:  Jakub Jozwicki <jozwicki@...er.pl>
> 
> --- linux-2.6.25.10/kernel/pm_qos_params.c	2008-07-03 05:46:47.000000000 +0200
> +++ linux-2.6.25.10-rt7/kernel/pm_qos_params.c	2008-07-12 23:18:20.696615771 
> +0200
> @@ -110,7 +110,7 @@
>  	&network_throughput_pm_qos
>  };
>  
> -static DEFINE_SPINLOCK(pm_qos_lock);
> +static DEFINE_RWLOCK(pm_qos_lock);

I don't see a problem with using spinlocks, and as this issues only
shows up running the PREEMPT-RT I feel that perhaps this would be better
in the RT tree.

Sorry,

--mgross


>  
>  static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf,
>  		size_t count, loff_t *f_pos);
> @@ -142,7 +142,7 @@
>  	unsigned long flags;
>  	int call_notifier = 0;
>  
> -	spin_lock_irqsave(&pm_qos_lock, flags);
> +	write_lock_irqsave(&pm_qos_lock, flags);
>  	extreme_value = pm_qos_array[target]->default_value;
>  	list_for_each_entry(node,
>  			&pm_qos_array[target]->requirements.list, list) {
> @@ -155,7 +155,7 @@
>  		pr_debug(KERN_ERR "new target for qos %d is %d\n", target,
>  			pm_qos_array[target]->target_value);
>  	}
> -	spin_unlock_irqrestore(&pm_qos_lock, flags);
> +	write_unlock_irqrestore(&pm_qos_lock, flags);
>  
>  	if (call_notifier)
>  		blocking_notifier_call_chain(pm_qos_array[target]->notifiers,
> @@ -195,9 +195,9 @@
>  	int ret_val;
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&pm_qos_lock, flags);
> +	read_lock_irqsave(&pm_qos_lock, flags);
>  	ret_val = pm_qos_array[pm_qos_class]->target_value;
> -	spin_unlock_irqrestore(&pm_qos_lock, flags);
> +	read_unlock_irqrestore(&pm_qos_lock, flags);
>  
>  	return ret_val;
>  }
> @@ -228,10 +228,10 @@
>  		if (!dep->name)
>  			goto cleanup;
>  
> -		spin_lock_irqsave(&pm_qos_lock, flags);
> +		write_lock_irqsave(&pm_qos_lock, flags);
>  		list_add(&dep->list,
>  			&pm_qos_array[pm_qos_class]->requirements.list);
> -		spin_unlock_irqrestore(&pm_qos_lock, flags);
> +		write_unlock_irqrestore(&pm_qos_lock, flags);
>  		update_target(pm_qos_class);
>  
>  		return 0;
> @@ -260,7 +260,7 @@
>  	struct requirement_list *node;
>  	int pending_update = 0;
>  
> -	spin_lock_irqsave(&pm_qos_lock, flags);
> +	write_lock_irqsave(&pm_qos_lock, flags);
>  	list_for_each_entry(node,
>  		&pm_qos_array[pm_qos_class]->requirements.list, list) {
>  		if (strcmp(node->name, name) == 0) {
> @@ -273,7 +273,7 @@
>  			break;
>  		}
>  	}
> -	spin_unlock_irqrestore(&pm_qos_lock, flags);
> +	write_unlock_irqrestore(&pm_qos_lock, flags);
>  	if (pending_update)
>  		update_target(pm_qos_class);
>  
> @@ -295,7 +295,7 @@
>  	struct requirement_list *node;
>  	int pending_update = 0;
>  
> -	spin_lock_irqsave(&pm_qos_lock, flags);
> +	write_lock_irqsave(&pm_qos_lock, flags);
>  	list_for_each_entry(node,
>  		&pm_qos_array[pm_qos_class]->requirements.list, list) {
>  		if (strcmp(node->name, name) == 0) {
> @@ -306,7 +306,7 @@
>  			break;
>  		}
>  	}
> -	spin_unlock_irqrestore(&pm_qos_lock, flags);
> +	write_unlock_irqrestore(&pm_qos_lock, flags);
>  	if (pending_update)
>  		update_target(pm_qos_class);
>  }
--
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