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

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Date:	Thu, 16 Jan 2014 02:17:01 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	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>
Subject: Re: [PATCH 1/3] pm/qos: allow state control of qos class

On Wednesday, November 27, 2013 12:28:16 AM Rafael J. Wysocki wrote:
> 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.

So the reason I don't like this patch is mainly because it affects all of the
users of struct pm_qos_constraints and pm_qos_read_value(), which include
device PM QoS among other things, but it only really needs to affect 
PM_QOS_CPU_DMA_LATENCY.

I would add a special routine, say pm_qos_cpu_dma_latency(), for reading the
current effective PM_QOS_CPU_DMA_LATENCY constraint and checking whether or
not it should be ignored.  Then, I'd make cpuidle use that.

Thanks!

> > ---
> >   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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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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