linux-kernel - Re: [PATCH 1/3] pm/qos: allow state control of qos class

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Date:	Wed, 27 Nov 2013 00:28:16 +0100
From:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
CC:	Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Len Brown <len.brown@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Zhang Rui <rui.zhang@...el.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH 1/3] pm/qos: allow state control of qos class

On 11/27/2013 12:20 AM, Jacob Pan wrote:
> When power capping or thermal control is needed, CPU QOS latency cannot
> be satisfied. This patch adds a state variable to indicate whether a QOS
> class (including all constraint requests) should be ignored.
>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>

Honestly, I don't like this.  I know the motivation and what you're 
trying to achieve, but I don't like the approach.

I need to think a bit more about that.

Thanks,
Rafael


> ---
>   include/linux/pm_qos.h | 10 +++++++++-
>   kernel/power/qos.c     | 24 ++++++++++++++++++++++++
>   2 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
> index 5a95013..648b50b 100644
> --- a/include/linux/pm_qos.h
> +++ b/include/linux/pm_qos.h
> @@ -10,7 +10,7 @@
>   #include <linux/device.h>
>   #include <linux/workqueue.h>
>   
> -enum {
> +enum pm_qos_class {
>   	PM_QOS_RESERVED = 0,
>   	PM_QOS_CPU_DMA_LATENCY,
>   	PM_QOS_NETWORK_LATENCY,
> @@ -20,6 +20,11 @@ enum {
>   	PM_QOS_NUM_CLASSES,
>   };
>   
> +enum pm_qos_state {
> +	PM_QOS_CONSTRAINT_AVAILABLE,
> +	PM_QOS_CONSTRAINT_IGNORED,
> +};
> +
>   enum pm_qos_flags_status {
>   	PM_QOS_FLAGS_UNDEFINED = -1,
>   	PM_QOS_FLAGS_NONE,
> @@ -77,6 +82,7 @@ struct pm_qos_constraints {
>   	struct plist_head list;
>   	s32 target_value;	/* Do not change to 64 bit */
>   	s32 default_value;
> +	enum pm_qos_state state;
>   	enum pm_qos_type type;
>   	struct blocking_notifier_head *notifiers;
>   };
> @@ -123,6 +129,8 @@ int pm_qos_add_notifier(int pm_qos_class, struct notifier_block *notifier);
>   int pm_qos_remove_notifier(int pm_qos_class, struct notifier_block *notifier);
>   int pm_qos_request_active(struct pm_qos_request *req);
>   s32 pm_qos_read_value(struct pm_qos_constraints *c);
> +void pm_qos_set_constraint_class_state(enum pm_qos_class class,
> +				enum pm_qos_state state);
>   
>   #ifdef CONFIG_PM
>   enum pm_qos_flags_status __dev_pm_qos_flags(struct device *dev, s32 mask);
> diff --git a/kernel/power/qos.c b/kernel/power/qos.c
> index 8dff9b4..cf475b0 100644
> --- a/kernel/power/qos.c
> +++ b/kernel/power/qos.c
> @@ -146,6 +146,11 @@ static inline int pm_qos_get_value(struct pm_qos_constraints *c)
>   
>   s32 pm_qos_read_value(struct pm_qos_constraints *c)
>   {
> +	/* return invalid default value if constraints cannot be met, e.g.
> +	 * during idle injection.
> +	 */
> +	if (c->state == PM_QOS_CONSTRAINT_IGNORED)
> +		return PM_QOS_DEFAULT_VALUE;
>   	return c->target_value;
>   }
>   
> @@ -353,6 +358,25 @@ void pm_qos_add_request(struct pm_qos_request *req,
>   }
>   EXPORT_SYMBOL_GPL(pm_qos_add_request);
>   
> +void pm_qos_set_constraint_class_state(enum pm_qos_class class,
> +				enum pm_qos_state state)
> +{
> +	struct pm_qos_constraints *c = pm_qos_array[class]->constraints;
> +	unsigned long curr_value;
> +
> +	if (c->state == state)
> +		return;
> +	curr_value = (state == PM_QOS_CONSTRAINT_IGNORED) ?
> +		PM_QOS_DEFAULT_VALUE : c->target_value;
> +	c->state = state;
> +
> +	/* notify existing QOS requests change */
> +	blocking_notifier_call_chain(c->notifiers,
> +				curr_value,
> +				NULL);
> +}
> +EXPORT_SYMBOL_GPL(pm_qos_set_constraint_class_state);
> +
>   /**
>    * pm_qos_update_request - modifies an existing qos request
>    * @req : handle to list element holding a pm_qos request to use

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