Commit 6dbf5cea authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

cpuidle: menu: Avoid taking spinlock for accessing QoS values 



After commit 9908859a (cpuidle/menu: add per CPU PM QoS resume
latency consideration) the cpuidle menu governor calls
dev_pm_qos_read_value() on CPU devices to read the current resume
latency QoS constraint values for them.  That function takes a spinlock
to prevent the device's power.qos pointer from becoming NULL during
the access which is a problem for the RT patchset where spinlocks are
converted into mutexes and the idle loop stops working.

However, it is not even necessary for the menu governor to take
that spinlock, because the power.qos pointer accessed under it
cannot be modified during the access anyway.

For this reason, introduce a "raw" routine for accessing device
QoS resume latency constraints without locking and use it in the
menu governor.

Fixes: 9908859a (cpuidle/menu: add per CPU PM QoS resume latency consideration)
Acked-by: default avatarAlex Shi <alex.shi@linaro.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 37efa4b4

drivers/base/power/qos.c

+1 −2
Original line number Diff line number Diff line
@@ -108,8 +108,7 @@ s32 __dev_pm_qos_read_value(struct device *dev) 
{

	lockdep_assert_held(&dev->power.lock);



	return IS_ERR_OR_NULL(dev->power.qos) ?

		0 : pm_qos_read_value(&dev->power.qos->resume_latency);

	return dev_pm_qos_raw_read_value(dev);

}



/**

drivers/cpuidle/governors/menu.c

+1 −1
Original line number Diff line number Diff line
@@ -287,7 +287,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) 
	unsigned int interactivity_req;

	unsigned int expected_interval;

	unsigned long nr_iowaiters, cpu_load;

	int resume_latency = dev_pm_qos_read_value(device);

	int resume_latency = dev_pm_qos_raw_read_value(device);



	if (data->needs_update) {

		menu_update(drv, dev);

include/linux/pm_qos.h

+7 −0
Original line number Diff line number Diff line
@@ -173,6 +173,12 @@ static inline s32 dev_pm_qos_requested_flags(struct device *dev) 
{

	return dev->power.qos->flags_req->data.flr.flags;

}



static inline s32 dev_pm_qos_raw_read_value(struct device *dev)

{

	return IS_ERR_OR_NULL(dev->power.qos) ?

		0 : pm_qos_read_value(&dev->power.qos->resume_latency);

}

#else

static inline enum pm_qos_flags_status __dev_pm_qos_flags(struct device *dev,

							  s32 mask)
@@ -237,6 +243,7 @@ static inline void dev_pm_qos_hide_latency_tolerance(struct device *dev) {} 


static inline s32 dev_pm_qos_requested_resume_latency(struct device *dev) { return 0; }

static inline s32 dev_pm_qos_requested_flags(struct device *dev) { return 0; }

static inline s32 dev_pm_qos_raw_read_value(struct device *dev) { return 0; }

#endif



#endif

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