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Subject[RFC/RFT][PATCH v3 5/5] PM / runtime: Optimize the use of device links
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

If the device has no links to suppliers that should be used for
runtime PM (links with DEVICE_LINK_PM_RUNTIME set), there is no
reason to walk the list of suppliers for that device during
runtime suspend and resume.

Add a simple mechanism to detect that case and possibly avoid the
extra unnecessary overhead.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/base/core.c | 20 +++++++++++++-------
drivers/base/power/runtime.c | 23 ++++++++++++++++++++---
include/linux/pm.h | 1 +
include/linux/pm_runtime.h | 4 ++++
4 files changed, 38 insertions(+), 10 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -150,14 +150,17 @@ struct device_link *device_link_add(stru
if (!link)
goto out;

- if ((flags & DEVICE_LINK_PM_RUNTIME) && (flags & DEVICE_LINK_RPM_ACTIVE)) {
- if (pm_runtime_get_sync(supplier) < 0) {
- pm_runtime_put_noidle(supplier);
- kfree(link);
- link = NULL;
- goto out;
+ if (flags & DEVICE_LINK_PM_RUNTIME) {
+ if (flags & DEVICE_LINK_RPM_ACTIVE) {
+ if (pm_runtime_get_sync(supplier) < 0) {
+ pm_runtime_put_noidle(supplier);
+ kfree(link);
+ link = NULL;
+ goto out;
+ }
+ link->rpm_active = true;
}
- link->rpm_active = true;
+ pm_runtime_new_link(consumer);
}
get_device(supplier);
link->supplier = supplier;
@@ -207,6 +210,9 @@ static void __device_link_del(struct dev
dev_info(link->consumer, "Dropping the link to %s\n",
dev_name(link->supplier));

+ if (link->flags & DEVICE_LINK_PM_RUNTIME)
+ pm_runtime_drop_link(link->consumer);
+
list_del_rcu(&link->s_node);
list_del_rcu(&link->c_node);
call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -305,6 +305,7 @@ static int __rpm_callback(int (*cb)(stru
__releases(&dev->power.lock) __acquires(&dev->power.lock)
{
int retval, idx;
+ bool use_links = dev->power.links_count > 0;

if (dev->power.irq_safe) {
spin_unlock(&dev->power.lock);
@@ -318,7 +319,7 @@ static int __rpm_callback(int (*cb)(stru
* routine returns, so it is safe to read the status outside of
* the lock.
*/
- if (dev->power.runtime_status == RPM_RESUMING) {
+ if (use_links && dev->power.runtime_status == RPM_RESUMING) {
idx = device_links_read_lock();

retval = rpm_get_suppliers(dev);
@@ -341,8 +342,9 @@ static int __rpm_callback(int (*cb)(stru
*
* Do that if resume fails too.
*/
- if ((dev->power.runtime_status == RPM_SUSPENDING && !retval)
- || (dev->power.runtime_status == RPM_RESUMING && retval)) {
+ if (use_links
+ && ((dev->power.runtime_status == RPM_SUSPENDING && !retval)
+ || (dev->power.runtime_status == RPM_RESUMING && retval))) {
idx = device_links_read_lock();

fail:
@@ -1557,6 +1559,21 @@ void pm_runtime_clean_up_links(struct de
device_links_read_unlock(idx);
}

+void pm_runtime_new_link(struct device *dev)
+{
+ spin_lock_irq(&dev->power.lock);
+ dev->power.links_count++;
+ spin_unlock_irq(&dev->power.lock);
+}
+
+void pm_runtime_drop_link(struct device *dev)
+{
+ spin_lock_irq(&dev->power.lock);
+ WARN_ON(dev->power.links_count == 0);
+ dev->power.links_count--;
+ spin_unlock_irq(&dev->power.lock);
+}
+
/**
* pm_runtime_force_suspend - Force a device into suspend state if needed.
* @dev: Device to suspend.
Index: linux-pm/include/linux/pm.h
===================================================================
--- linux-pm.orig/include/linux/pm.h
+++ linux-pm/include/linux/pm.h
@@ -596,6 +596,7 @@ struct dev_pm_info {
unsigned int use_autosuspend:1;
unsigned int timer_autosuspends:1;
unsigned int memalloc_noio:1;
+ unsigned int links_count;
enum rpm_request request;
enum rpm_status runtime_status;
int runtime_error;
Index: linux-pm/include/linux/pm_runtime.h
===================================================================
--- linux-pm.orig/include/linux/pm_runtime.h
+++ linux-pm/include/linux/pm_runtime.h
@@ -56,6 +56,8 @@ extern void pm_runtime_update_max_time_s
s64 delta_ns);
extern void pm_runtime_set_memalloc_noio(struct device *dev, bool enable);
extern void pm_runtime_clean_up_links(struct device *dev);
+extern void pm_runtime_new_link(struct device *dev);
+extern void pm_runtime_drop_link(struct device *dev);

static inline void pm_suspend_ignore_children(struct device *dev, bool enable)
{
@@ -188,6 +190,8 @@ static inline unsigned long pm_runtime_a
static inline void pm_runtime_set_memalloc_noio(struct device *dev,
bool enable){}
static inline void pm_runtime_clean_up_links(struct device *dev) {}
+static inline void pm_runtime_new_link(struct device *dev) {}
+static inline void pm_runtime_drop_link(struct device *dev) {}

#endif /* !CONFIG_PM */

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