cpuidle: menu: Avoid taking spinlock for accessing QoS values

After commit 9908859acaa9 (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: 9908859acaa9 (cpuidle/menu: add per CPU PM QoS resume latency consideration)
Acked-by: Alex Shi <alex.shi@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
index 58fcc758334e5bd230a5929a70844d35f4615628..73142d0862403702aaee1bd5a16e5669e40907d9 100644 (file)
--- a/drivers/base/power/qos.c
+++ b/drivers/base/power/qos.c
@@ -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);
 }
 
 /**

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 8d6d25c38c020e1bcc6f6f0e68d8aab97f96bc3d..6d6f46e79d94958b83920da3dec2ec47301e2f78 100644 (file)
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -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);

diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
index 0f65d36c2a75153c4f0c1b47f2ff351ca5365239..5aba9f47899d2bd820dcf75a8ede1e73b307b429 100644 (file)
--- a/include/linux/pm_qos.h
+++ b/include/linux/pm_qos.h
@@ -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