linux-kernel - [PATCH v2] pmdomain: governor: Consider CPU latency tolerance from pm_domain_cpu

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Message-Id: <20250709-pmdomain_qos-v2-1-976b12257899@oss.qualcomm.com>
Date: Wed, 09 Jul 2025 14:00:11 +0530
From: Maulik Shah <maulik.shah@....qualcomm.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Maulik Shah <maulik.shah@....qualcomm.com>
Subject: [PATCH v2] pmdomain: governor: Consider CPU latency tolerance from
 pm_domain_cpu_gov

pm_domain_cpu_gov is selecting a cluster idle state but does not consider
latency tolerance of child CPUs. This results in deeper cluster idle state
whose latency does not meet latency tolerance requirement.

Select deeper idle state only if global and device latency tolerance of all
child CPUs meet.

Test results on SM8750 with 300 usec PM-QoS on CPU0 which is less than
domain idle state entry (2150) + exit (1983) usec latency mentioned in
devicetree, demonstrate the issue.

	# echo 300 > /sys/devices/system/cpu/cpu0/power/pm_qos_resume_latency_us

Before: (Usage is incrementing)
======
	# cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
	State          Time Spent(ms) Usage      Rejected   Above      Below
	S0             29817          537        8          270        0

	# cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
	State          Time Spent(ms) Usage      Rejected   Above      Below
	S0             30348          542        8          271        0

After: (Usage is not incrementing due to latency tolerance)
======
	# cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
	State          Time Spent(ms) Usage      Rejected   Above      Below
	S0             39319          626        14         307        0

	# cat /sys/kernel/debug/pm_genpd/power-domain-cluster0/idle_states
	State          Time Spent(ms) Usage      Rejected   Above      Below
	S0             39319          626        14         307        0

Signed-off-by: Maulik Shah <maulik.shah@....qualcomm.com>
---
Changes in v2:
- Rename device pointer to cpu_dev
- Replace dev_pm_qos_read_value() with dev_pm_qos_raw_resume_latency()
- Link to v1: https://lore.kernel.org/all/20250708-pmdomain_qos-v1-1-7c502f4c901a@oss.qualcomm.com
---
 drivers/pmdomain/governor.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/pmdomain/governor.c b/drivers/pmdomain/governor.c
index c1e148657c873a6b5b4d9c0f058d54cb020c56e2..39359811a93047b36443a1b9583962726f24b88b 100644
--- a/drivers/pmdomain/governor.c
+++ b/drivers/pmdomain/governor.c
@@ -8,6 +8,7 @@
 #include <linux/pm_domain.h>
 #include <linux/pm_qos.h>
 #include <linux/hrtimer.h>
+#include <linux/cpu.h>
 #include <linux/cpuidle.h>
 #include <linux/cpumask.h>
 #include <linux/ktime.h>
@@ -349,6 +350,8 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	struct cpuidle_device *dev;
 	ktime_t domain_wakeup, next_hrtimer;
 	ktime_t now = ktime_get();
+	struct device *cpu_dev;
+	s64 cpu_constraint, global_constraint;
 	s64 idle_duration_ns;
 	int cpu, i;
 
@@ -359,6 +362,7 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN))
 		return true;
 
+	global_constraint = cpu_latency_qos_limit();
 	/*
 	 * Find the next wakeup for any of the online CPUs within the PM domain
 	 * and its subdomains. Note, we only need the genpd->cpus, as it already
@@ -372,8 +376,16 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 			if (ktime_before(next_hrtimer, domain_wakeup))
 				domain_wakeup = next_hrtimer;
 		}
+
+		cpu_dev = get_cpu_device(cpu);
+		if (cpu_dev) {
+			cpu_constraint = dev_pm_qos_raw_resume_latency(cpu_dev);
+			if (cpu_constraint < global_constraint)
+				global_constraint = cpu_constraint;
+		}
 	}
 
+	global_constraint *= NSEC_PER_USEC;
 	/* The minimum idle duration is from now - until the next wakeup. */
 	idle_duration_ns = ktime_to_ns(ktime_sub(domain_wakeup, now));
 	if (idle_duration_ns <= 0)
@@ -389,8 +401,10 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	 */
 	i = genpd->state_idx;
 	do {
-		if (idle_duration_ns >= (genpd->states[i].residency_ns +
-		    genpd->states[i].power_off_latency_ns)) {
+		if ((idle_duration_ns >= (genpd->states[i].residency_ns +
+		    genpd->states[i].power_off_latency_ns)) &&
+		    (global_constraint >= (genpd->states[i].power_on_latency_ns +
+		    genpd->states[i].power_off_latency_ns))) {
 			genpd->state_idx = i;
 			genpd->gd->last_enter = now;
 			genpd->gd->reflect_residency = true;

---
base-commit: 26ffb3d6f02cd0935fb9fa3db897767beee1cb2a
change-id: 20250708-pmdomain_qos-29077f8b622e

Best regards,
-- 
Maulik Shah <maulik.shah@....qualcomm.com>