[RFC] pm_qos: reimplement using plists

James Bottomley
2010-06-05T17:58:08Z

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.

There is one nasty that should probably be fixed in plists not open
coded here: plist_first gives the highest priority value, but there's no
corresponding API to give the lowest (even though you can get it from
the head.nodes_list.prev) ... if the sched people are OK, I'll correct
this with the final patch set.

James

---

kernel/pm_qos_params.c | 152 +++++++++++++++++++++++-------------------------
1 files changed, 73 insertions(+), 79 deletions(-)

diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
index f42d3f7..241fa79 100644
--- a/kernel/pm_qos_params.c
+++ b/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 +50,51 @@
* 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 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)},
.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)},
.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)},
.notifiers = &network_throughput_notifier,
.name = "network_throughput",
.default_value = 0,
- .target_value = ATOMIC_INIT(0),
- .comparitor = max_compare
+ .type = PM_QOS_MAX,
};

@@ -124,46 +118,40 @@ 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 list_entry(o->requests.node_list.prev, struct plist_node, plist.node_list)->prio;

+ case PM_QOS_MAX:
+ return plist_first(&o->requests)->prio;
+ }
+}

-static void update_target(int pm_qos_class)
+static void update_target(struct pm_qos_object *o, struct plist_node *node,
+ int del)
{
- 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);
+ 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 +184,14 @@ 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 +209,19 @@ 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);
}

return dep;
@@ -251,22 +244,27 @@ void pm_qos_update_request(struct pm_qos_request_list *pm_qos_req,
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 (!pm_qos_req) /*guard against callers passing in null */
+ return;

- if (temp != pm_qos_req->value) {
- pending_update = 1;
- pm_qos_req->value = temp;
- }
+ 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) {
+ pending_update = 1;
+ spin_lock_irqsave(&pm_qos_lock, flags);
+ plist_del(&pm_qos_req->list, &o->requests);
+ plist_node_init(&pm_qos_req->list, temp);
spin_unlock_irqrestore(&pm_qos_lock, flags);
- if (pending_update)
- update_target(pm_qos_req->pm_qos_class);
}
+ if (pending_update)
+ update_target(o, &pm_qos_req->list, 0);
}
EXPORT_SYMBOL_GPL(pm_qos_update_request);

@@ -280,19 +278,15 @@ 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);
kfree(pm_qos_req);
- spin_unlock_irqrestore(&pm_qos_lock, flags);
- update_target(qos_class);
}
EXPORT_SYMBOL_GPL(pm_qos_remove_request);