linux-kernel - [PATCH v2 3/4] sched: idle: Respect the CPU system-wakeup QoS limit for s2idle

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Message-ID: <20251016151929.75863-4-ulf.hansson@linaro.org>
Date: Thu, 16 Oct 2025 17:19:23 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	linux-pm@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kevin Hilman <khilman@...libre.com>,
	Pavel Machek <pavel@...nel.org>,
	Len Brown <len.brown@...el.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Maulik Shah <quic_mkshah@...cinc.com>,
	Prasad Sodagudi <psodagud@...cinc.com>,
	Dhruva Gole <d-gole@...com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/4] sched: idle: Respect the CPU system-wakeup QoS limit for s2idle

A CPU system-wakeup QoS limit may have been requested by user-space. To
avoid breaking this constraint when entering a low-power state during
s2idle, let's start to take into account the QoS limit.

Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---

Changes in v2:
	- Rework the code to take into account the failure/error path, when we
	don't find a s2idle specific state.

---
 drivers/cpuidle/cpuidle.c | 12 +++++++-----
 include/linux/cpuidle.h   |  6 ++++--
 kernel/sched/idle.c       | 12 +++++++-----
 3 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 56132e843c99..c7876e9e024f 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -184,20 +184,22 @@ static noinstr void enter_s2idle_proper(struct cpuidle_driver *drv,
  * cpuidle_enter_s2idle - Enter an idle state suitable for suspend-to-idle.
  * @drv: cpuidle driver for the given CPU.
  * @dev: cpuidle device for the given CPU.
+ * @latency_limit_ns: Idle state exit latency limit
  *
  * If there are states with the ->enter_s2idle callback, find the deepest of
  * them and enter it with frozen tick.
  */
-int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
+int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
+			 u64 latency_limit_ns)
 {
 	int index;
 
 	/*
-	 * Find the deepest state with ->enter_s2idle present, which guarantees
-	 * that interrupts won't be enabled when it exits and allows the tick to
-	 * be frozen safely.
+	 * Find the deepest state with ->enter_s2idle present that meets the
+	 * specified latency limit, which guarantees that interrupts won't be
+	 * enabled when it exits and allows the tick to be frozen safely.
 	 */
-	index = find_deepest_state(drv, dev, U64_MAX, 0, true);
+	index = find_deepest_state(drv, dev, latency_limit_ns, 0, true);
 	if (index > 0) {
 		enter_s2idle_proper(drv, dev, index);
 		local_irq_enable();
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index a9ee4fe55dcf..4073690504a7 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -248,7 +248,8 @@ extern int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
 				      struct cpuidle_device *dev,
 				      u64 latency_limit_ns);
 extern int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
-				struct cpuidle_device *dev);
+				struct cpuidle_device *dev,
+				u64 latency_limit_ns);
 extern void cpuidle_use_deepest_state(u64 latency_limit_ns);
 #else
 static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
@@ -256,7 +257,8 @@ static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
 					     u64 latency_limit_ns)
 {return -ENODEV; }
 static inline int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
-				       struct cpuidle_device *dev)
+				       struct cpuidle_device *dev,
+				       u64 latency_limit_ns)
 {return -ENODEV; }
 static inline void cpuidle_use_deepest_state(u64 latency_limit_ns)
 {
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index c39b089d4f09..c1c3d0166610 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -131,12 +131,13 @@ void __cpuidle default_idle_call(void)
 }
 
 static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
-			       struct cpuidle_device *dev)
+			       struct cpuidle_device *dev,
+			       u64 max_latency_ns)
 {
 	if (current_clr_polling_and_test())
 		return -EBUSY;
 
-	return cpuidle_enter_s2idle(drv, dev);
+	return cpuidle_enter_s2idle(drv, dev, max_latency_ns);
 }
 
 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
@@ -205,12 +206,13 @@ static void cpuidle_idle_call(void)
 		u64 max_latency_ns;
 
 		if (idle_should_enter_s2idle()) {
+			max_latency_ns = cpu_wakeup_latency_qos_limit() *
+					 NSEC_PER_USEC;
 
-			entered_state = call_cpuidle_s2idle(drv, dev);
+			entered_state = call_cpuidle_s2idle(drv, dev,
+							    max_latency_ns);
 			if (entered_state > 0)
 				goto exit_idle;
-
-			max_latency_ns = U64_MAX;
 		} else {
 			max_latency_ns = dev->forced_idle_latency_limit_ns;
 		}
-- 
2.43.0