linux-kernel - [RFC/PATCH 3/3] cpuidle: Respect the system-wakeup QoS limit for s2idle

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Message-ID: <20250716123323.65441-4-ulf.hansson@linaro.org>
Date: Wed, 16 Jul 2025 14:33:19 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	linux-pm@...r.kernel.org
Cc: 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>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: [RFC/PATCH 3/3] cpuidle: Respect the system-wakeup QoS limit for s2idle

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

Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---
 drivers/cpuidle/cpuidle.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 0835da449db8..5f6dacb5b134 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -190,14 +190,15 @@ static noinstr void enter_s2idle_proper(struct cpuidle_driver *drv,
  */
 int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
+	u64 constraint_ns = system_wakeup_latency_qos_limit() * NSEC_PER_USEC;
 	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
+	 * system-wakeup QoS 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, constraint_ns, 0, true);
 	if (index > 0) {
 		enter_s2idle_proper(drv, dev, index);
 		local_irq_enable();
-- 
2.43.0