pm_qos: Reimplement using plists

A lot of the pm_qos extremal value handling is really duplicating what a
priority ordered list does, just in a less efficient fashion.  Simply
redoing the implementation in terms of a plist gets rid of a lot of this
junk (although there are several other strange things that could do with
tidying up, like pm_qos_request_list has to carry the pm_qos_class with
every node, simply because it doesn't get passed in to
pm_qos_update_request even though every caller knows full well what
parameter it's updating).

I think this redo is a win independent of android, so we should do
something like this now.
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Signed-off-by: mark gross <markgross@thegnar.org>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

kernel/pm_qos_params.c

@@ -30,6 +30,7 @@
 /*#define DEBUG*/
 
 #include <linux/pm_qos_params.h>
+#include <linux/plist.h>
 #include <linux/sched.h>
 #include <linux/spinlock.h>
 #include <linux/slab.h>
@@ -49,58 +50,53 @@
  * held, taken with _irqsave.  One lock to rule them all
  */
 struct pm_qos_request_list {
-	struct list_head list;
-	union {
-		s32 value;
-		s32 usec;
-		s32 kbps;
-	};
+	struct plist_node list;
 	int pm_qos_class;
 };
 
-static s32 max_compare(s32 v1, s32 v2);
-static s32 min_compare(s32 v1, s32 v2);
+enum pm_qos_type {
+	PM_QOS_MAX,		/* return the largest value */
+	PM_QOS_MIN		/* return the smallest value */
+};
 
 struct pm_qos_object {
-	struct pm_qos_request_list requests;
+	struct plist_head requests;
 	struct blocking_notifier_head *notifiers;
 	struct miscdevice pm_qos_power_miscdev;
 	char *name;
 	s32 default_value;
-	atomic_t target_value;
-	s32 (*comparitor)(s32, s32);
+	enum pm_qos_type type;
 };
 
+static DEFINE_SPINLOCK(pm_qos_lock);
+
 static struct pm_qos_object null_pm_qos;
 static BLOCKING_NOTIFIER_HEAD(cpu_dma_lat_notifier);
 static struct pm_qos_object cpu_dma_pm_qos = {
-	.requests = {LIST_HEAD_INIT(cpu_dma_pm_qos.requests.list)},
+	.requests = PLIST_HEAD_INIT(cpu_dma_pm_qos.requests, pm_qos_lock),
 	.notifiers = &cpu_dma_lat_notifier,
 	.name = "cpu_dma_latency",
 	.default_value = 2000 * USEC_PER_SEC,
-	.target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
-	.comparitor = min_compare
+	.type = PM_QOS_MIN,
 };
 
 static BLOCKING_NOTIFIER_HEAD(network_lat_notifier);
 static struct pm_qos_object network_lat_pm_qos = {
-	.requests = {LIST_HEAD_INIT(network_lat_pm_qos.requests.list)},
+	.requests = PLIST_HEAD_INIT(network_lat_pm_qos.requests, pm_qos_lock),
 	.notifiers = &network_lat_notifier,
 	.name = "network_latency",
 	.default_value = 2000 * USEC_PER_SEC,
-	.target_value = ATOMIC_INIT(2000 * USEC_PER_SEC),
-	.comparitor = min_compare
+	.type = PM_QOS_MIN
 };
 
 
 static BLOCKING_NOTIFIER_HEAD(network_throughput_notifier);
 static struct pm_qos_object network_throughput_pm_qos = {
-	.requests = {LIST_HEAD_INIT(network_throughput_pm_qos.requests.list)},
+	.requests = PLIST_HEAD_INIT(network_throughput_pm_qos.requests, pm_qos_lock),
 	.notifiers = &network_throughput_notifier,
 	.name = "network_throughput",
 	.default_value = 0,
-	.target_value = ATOMIC_INIT(0),
-	.comparitor = max_compare
+	.type = PM_QOS_MAX,
 };
 
 
@@ -111,8 +107,6 @@ static struct pm_qos_object *pm_qos_array[] = {
 	&network_throughput_pm_qos
 };
 
-static DEFINE_SPINLOCK(pm_qos_lock);
-
 static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf,
 		size_t count, loff_t *f_pos);
 static int pm_qos_power_open(struct inode *inode, struct file *filp);
@@ -124,46 +118,55 @@ static const struct file_operations pm_qos_power_fops = {
 	.release = pm_qos_power_release,
 };
 
-/* static helper functions */
-static s32 max_compare(s32 v1, s32 v2)
+/* unlocked internal variant */
+static inline int pm_qos_get_value(struct pm_qos_object *o)
 {
-	return max(v1, v2);
-}
+	if (plist_head_empty(&o->requests))
+		return o->default_value;
 
-static s32 min_compare(s32 v1, s32 v2)
-{
-	return min(v1, v2);
-}
+	switch (o->type) {
+	case PM_QOS_MIN:
+		return plist_last(&o->requests)->prio;
 
+	case PM_QOS_MAX:
+		return plist_first(&o->requests)->prio;
 
-static void update_target(int pm_qos_class)
+	default:
+		/* runtime check for not using enum */
+		BUG();
+	}
+}
+
+static void update_target(struct pm_qos_object *o, struct plist_node *node,
+			  int del, int value)
 {
-	s32 extreme_value;
-	struct pm_qos_request_list *node;
 	unsigned long flags;
-	int call_notifier = 0;
+	int prev_value, curr_value;
 
 	spin_lock_irqsave(&pm_qos_lock, flags);
-	extreme_value = pm_qos_array[pm_qos_class]->default_value;
-	list_for_each_entry(node,
-			&pm_qos_array[pm_qos_class]->requests.list, list) {
-		extreme_value = pm_qos_array[pm_qos_class]->comparitor(
-				extreme_value, node->value);
-	}
-	if (atomic_read(&pm_qos_array[pm_qos_class]->target_value) !=
-			extreme_value) {
-		call_notifier = 1;
-		atomic_set(&pm_qos_array[pm_qos_class]->target_value,
-				extreme_value);
-		pr_debug(KERN_ERR "new target for qos %d is %d\n", pm_qos_class,
-			atomic_read(&pm_qos_array[pm_qos_class]->target_value));
+	prev_value = pm_qos_get_value(o);
+	/* PM_QOS_DEFAULT_VALUE is a signal that the value is unchanged */
+	if (value != PM_QOS_DEFAULT_VALUE) {
+		/*
+		 * to change the list, we atomically remove, reinit
+		 * with new value and add, then see if the extremal
+		 * changed
+		 */
+		plist_del(node, &o->requests);
+		plist_node_init(node, value);
+		plist_add(node, &o->requests);
+	} else if (del) {
+		plist_del(node, &o->requests);
+	} else {
+		plist_add(node, &o->requests);
 	}
+	curr_value = pm_qos_get_value(o);
 	spin_unlock_irqrestore(&pm_qos_lock, flags);
 
-	if (call_notifier)
-		blocking_notifier_call_chain(
-				pm_qos_array[pm_qos_class]->notifiers,
-					(unsigned long) extreme_value, NULL);
+	if (prev_value != curr_value)
+		blocking_notifier_call_chain(o->notifiers,
+					     (unsigned long)curr_value,
+					     NULL);
 }
 
 static int register_pm_qos_misc(struct pm_qos_object *qos)
@@ -196,7 +199,14 @@ static int find_pm_qos_object_by_minor(int minor)
  */
 int pm_qos_request(int pm_qos_class)
 {
-	return atomic_read(&pm_qos_array[pm_qos_class]->target_value);
+	unsigned long flags;
+	int value;
+
+	spin_lock_irqsave(&pm_qos_lock, flags);
+	value = pm_qos_get_value(pm_qos_array[pm_qos_class]);
+	spin_unlock_irqrestore(&pm_qos_lock, flags);
+
+	return value;
 }
 EXPORT_SYMBOL_GPL(pm_qos_request);
 
@@ -214,21 +224,19 @@ EXPORT_SYMBOL_GPL(pm_qos_request);
 struct pm_qos_request_list *pm_qos_add_request(int pm_qos_class, s32 value)
 {
 	struct pm_qos_request_list *dep;
-	unsigned long flags;
 
 	dep = kzalloc(sizeof(struct pm_qos_request_list), GFP_KERNEL);
 	if (dep) {
+		struct pm_qos_object *o =  pm_qos_array[pm_qos_class];
+		int new_value;
+
 		if (value == PM_QOS_DEFAULT_VALUE)
-			dep->value = pm_qos_array[pm_qos_class]->default_value;
+			new_value = o->default_value;
 		else
-			dep->value = value;
+			new_value = value;
+		plist_node_init(&dep->list, new_value);
 		dep->pm_qos_class = pm_qos_class;
-
-		spin_lock_irqsave(&pm_qos_lock, flags);
-		list_add(&dep->list,
-			&pm_qos_array[pm_qos_class]->requests.list);
-		spin_unlock_irqrestore(&pm_qos_lock, flags);
-		update_target(pm_qos_class);
+		update_target(o, &dep->list, 0, PM_QOS_DEFAULT_VALUE);
 	}
 
 	return dep;
@@ -246,27 +254,23 @@ EXPORT_SYMBOL_GPL(pm_qos_add_request);
  * Attempts are made to make this code callable on hot code paths.
  */
 void pm_qos_update_request(struct pm_qos_request_list *pm_qos_req,
-		s32 new_value)
+			   s32 new_value)
 {
-	unsigned long flags;
-	int pending_update = 0;
 	s32 temp;
+	struct pm_qos_object *o;
 
-	if (pm_qos_req) { /*guard against callers passing in null */
-		spin_lock_irqsave(&pm_qos_lock, flags);
-		if (new_value == PM_QOS_DEFAULT_VALUE)
-			temp = pm_qos_array[pm_qos_req->pm_qos_class]->default_value;
-		else
-			temp = new_value;
-
-		if (temp != pm_qos_req->value) {
-			pending_update = 1;
-			pm_qos_req->value = temp;
-		}
-		spin_unlock_irqrestore(&pm_qos_lock, flags);
-		if (pending_update)
-			update_target(pm_qos_req->pm_qos_class);
-	}
+	if (!pm_qos_req) /*guard against callers passing in null */
+		return;
+
+	o = pm_qos_array[pm_qos_req->pm_qos_class];
+
+	if (new_value == PM_QOS_DEFAULT_VALUE)
+		temp = o->default_value;
+	else
+		temp = new_value;
+
+	if (temp != pm_qos_req->list.prio)
+		update_target(o, &pm_qos_req->list, 0, temp);
 }
 EXPORT_SYMBOL_GPL(pm_qos_update_request);
 
@@ -280,19 +284,15 @@ EXPORT_SYMBOL_GPL(pm_qos_update_request);
  */
 void pm_qos_remove_request(struct pm_qos_request_list *pm_qos_req)
 {
-	unsigned long flags;
-	int qos_class;
+	struct pm_qos_object *o;
 
 	if (pm_qos_req == NULL)
 		return;
 		/* silent return to keep pcm code cleaner */
 
-	qos_class = pm_qos_req->pm_qos_class;
-	spin_lock_irqsave(&pm_qos_lock, flags);
-	list_del(&pm_qos_req->list);
+	o = pm_qos_array[pm_qos_req->pm_qos_class];
+	update_target(o, &pm_qos_req->list, 1, PM_QOS_DEFAULT_VALUE);
 	kfree(pm_qos_req);
-	spin_unlock_irqrestore(&pm_qos_lock, flags);
-	update_target(qos_class);
 }
 EXPORT_SYMBOL_GPL(pm_qos_remove_request);