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

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Message-Id: <20250708-pmdomain_qos-v1-1-7c502f4c901a@oss.qualcomm.com>
Date: Tue, 08 Jul 2025 10:45:22 +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] 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>
---
 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..d5ac4c1b5b5a432f0072209d17379e58ec891202 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 *device;
+	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;
 		}
+
+		device = get_cpu_device(cpu);
+		if (device) {
+			cpu_constraint = dev_pm_qos_read_value(device, DEV_PM_QOS_RESUME_LATENCY);
+			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: 50c8770a42faf8b1c7abe93e7c114337f580a97d
change-id: 20250703-pmdomain_qos-25b8dbb623ea

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