[PATCH v6 3/3] PM / Domains: use device's next wakeup to determine domain idle state

[Lina Iyer <ilina@codeaurora.org>]

Currently, a PM domain's idle state is determined based on whether the
QoS requirements are met. This may not save power, if the idle state
residency requirements are not met.

CPU PM domains use the next timer wakeup for the CPUs in the domain to
determine the sleep duration of the domain. This is compared with the
idle state residencies to determine the optimal idle state. For other PM
domains, determining the sleep length is not that straight forward. But
if the device's next_event is available, we can use that to determine
the sleep duration of the PM domain.

Let's update the domain governor logic to check for idle state residency
based on the next wakeup of devices as well as QoS constraints.

Signed-off-by: Lina Iyer <ilina@codeaurora.org>
---
Changes in v6:
	- Do not include power_on_latency_ns for next_wakeup
	  determination.
	- Re-organize code to avoid multiple ktime_get() reads.
	- Check genpd flag if next_wakeup is useful for the domain.
	- Document why we ignore stale data
Changes in v5:
	- Minor code changes suggested by Rafel
Changes in v4:
	- Update to use next_wakeup from struct generic_pm_domain_data.
Changes in v3:
	- None
Changes in v2:
	- Fix state_idx type to hold negative value.
	- Update commit text.
---
 drivers/base/power/domain_governor.c | 102 ++++++++++++++++++++++++---
 include/linux/pm_domain.h            |   1 +
 2 files changed, 94 insertions(+), 9 deletions(-)

diff --git a/drivers/base/power/domain_governor.c b/drivers/base/power/domain_governor.c
index 490ed7deb99a..2afb7fa90d5d 100644
--- a/drivers/base/power/domain_governor.c
+++ b/drivers/base/power/domain_governor.c
@@ -117,6 +117,55 @@ static bool default_suspend_ok(struct device *dev)
 	return td->cached_suspend_ok;
 }
 
+static void update_domain_next_wakeup(struct generic_pm_domain *genpd, ktime_t now)
+{
+	ktime_t domain_wakeup = KTIME_MAX;
+	ktime_t next_wakeup;
+	struct pm_domain_data *pdd;
+	struct gpd_link *link;
+
+	if (!genpd_may_use_next_wakeup(genpd))
+		return;
+
+	/*
+	 * Devices that have a predictable wakeup pattern, may specify
+	 * their next wakeup. Let's find the next wakeup from all the
+	 * devices attached to this domain and from all the sub-domains.
+	 * It is possible that component's a next wakeup may have become
+	 * stale when we read that here. We will ignore to ensure the domain
+	 * is able to enter its optimal idle state.
+	 */
+	list_for_each_entry(pdd, &genpd->dev_list, list_node) {
+		next_wakeup = to_gpd_data(pdd)->next_wakeup;
+		if (next_wakeup != KTIME_MAX && !ktime_before(next_wakeup, now))
+			if (ktime_before(next_wakeup, domain_wakeup))
+				domain_wakeup = next_wakeup;
+	}
+
+	list_for_each_entry(link, &genpd->parent_links, parent_node) {
+		next_wakeup = link->child->next_wakeup;
+		if (next_wakeup != KTIME_MAX && !ktime_before(next_wakeup, now))
+			if (ktime_before(next_wakeup, domain_wakeup))
+				domain_wakeup = next_wakeup;
+	}
+
+	genpd->next_wakeup = domain_wakeup;
+}
+
+static bool next_wakeup_allows_state(struct generic_pm_domain *genpd,
+				     unsigned int state, ktime_t now)
+{
+	ktime_t domain_wakeup = genpd->next_wakeup;
+	s64 idle_time_ns, min_sleep_ns;
+
+	min_sleep_ns = genpd->states[state].power_off_latency_ns +
+		       genpd->states[state].residency_ns;
+
+	idle_time_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
+
+	return idle_time_ns >= min_sleep_ns;
+}
+
 static bool __default_power_down_ok(struct dev_pm_domain *pd,
 				     unsigned int state)
 {
@@ -201,16 +250,41 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd,
 }
 
 /**
- * default_power_down_ok - Default generic PM domain power off governor routine.
+ * _default_power_down_ok - Default generic PM domain power off governor routine.
  * @pd: PM domain to check.
  *
  * This routine must be executed under the PM domain's lock.
  */
-static bool default_power_down_ok(struct dev_pm_domain *pd)
+static bool _default_power_down_ok(struct dev_pm_domain *pd, ktime_t now)
 {
 	struct generic_pm_domain *genpd = pd_to_genpd(pd);
+	int state_idx = genpd->state_count - 1;
 	struct gpd_link *link;
 
+	/*
+	 * Find the next wakeup from devices that can determine their own wakeup
+	 * to find when the domain would wakeup and do it for every device down
+	 * the hierarchy. It is not worth while to sleep if the state's residency
+	 * cannot be met.
+	 */
+	update_domain_next_wakeup(genpd, now);
+	if (genpd->next_wakeup != KTIME_MAX) {
+		/* Let's find out the deepest domain idle state, the devices prefer */
+		while (state_idx >= 0) {
+			if (next_wakeup_allows_state(genpd, state_idx, now)) {
+				genpd->max_off_time_changed = true;
+				break;
+			}
+			state_idx--;
+		}
+
+		if (state_idx < 0) {
+			state_idx = 0;
+			genpd->cached_power_down_ok = false;
+			goto done;
+		}
+	}
+
 	if (!genpd->max_off_time_changed) {
 		genpd->state_idx = genpd->cached_power_down_state_idx;
 		return genpd->cached_power_down_ok;
@@ -228,21 +302,30 @@ static bool default_power_down_ok(struct dev_pm_domain *pd)
 	genpd->max_off_time_ns = -1;
 	genpd->max_off_time_changed = false;
 	genpd->cached_power_down_ok = true;
-	genpd->state_idx = genpd->state_count - 1;
 
-	/* Find a state to power down to, starting from the deepest. */
-	while (!__default_power_down_ok(pd, genpd->state_idx)) {
-		if (genpd->state_idx == 0) {
+	/*
+	 * Find a state to power down to, starting from the state
+	 * determined by the next wakeup.
+	 */
+	while (!__default_power_down_ok(pd, state_idx)) {
+		if (state_idx == 0) {
 			genpd->cached_power_down_ok = false;
 			break;
 		}
-		genpd->state_idx--;
+		state_idx--;
 	}
 
+done:
+	genpd->state_idx = state_idx;
 	genpd->cached_power_down_state_idx = genpd->state_idx;
 	return genpd->cached_power_down_ok;
 }
 
+static bool default_power_down_ok(struct dev_pm_domain *pd)
+{
+	return _default_power_down_ok(pd, ktime_get());
+}
+
 static bool always_on_power_down_ok(struct dev_pm_domain *domain)
 {
 	return false;
@@ -254,11 +337,12 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	struct generic_pm_domain *genpd = pd_to_genpd(pd);
 	struct cpuidle_device *dev;
 	ktime_t domain_wakeup, next_hrtimer;
+	ktime_t now = ktime_get();
 	s64 idle_duration_ns;
 	int cpu, i;
 
 	/* Validate dev PM QoS constraints. */
-	if (!default_power_down_ok(pd))
+	if (!_default_power_down_ok(pd, now))
 		return false;
 
 	if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN))
@@ -280,7 +364,7 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	}
 
 	/* The minimum idle duration is from now - until the next wakeup. */
-	idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, ktime_get()));
+	idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
 	if (idle_duration_ns <= 0)
 		return false;
 
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index cc27d3d88849..a41aea9d1c06 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -136,6 +136,7 @@ struct generic_pm_domain {
 				     unsigned int state);
 	struct gpd_dev_ops dev_ops;
 	s64 max_off_time_ns;	/* Maximum allowed "suspended" time. */
+	ktime_t next_wakeup;	/* Maintained by the domain governor */
 	bool max_off_time_changed;
 	bool cached_power_down_ok;
 	bool cached_power_down_state_idx;
-- 
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