[PATCH 0/3] PM: runtime: add new runtime metrics and summary

[PATCH 0/3] PM: runtime: add new runtime metrics and summary

[Joshua Crofts]

Add a new set additional PM runtime metrics to improve power management
debugging and reporting (these metrics may be useful to userspace
utilities such as Powertop).

MOTIVATION:
The current implementation only measures the duration a device spends in
suspended or active mode, which is very limiting. We can't find out how
many times a device changed state or what its shortest suspend cycle
was (to detect a sort of power "thrashing" behaviour).

NEW FEATURES:
This series introduces the following new metrics:
- resume_count : number of successful transitions to active
- suspend_count: number of successful transitions to suspended
- last_suspended_time: duration of the most recent sleep cycle (ns)
- min_suspended_time / max_suspended_sleep: shortest and longest sleep
  cycle durations to help detect power thrashing (ns)

By reading the debugfs file /sys/kernel/debug/pm_runtime_summary, you
get the following table describing the power stats of each device with
runtime PM enabled:

Device                           Status        Resumes Suspends   Active(ms)  Suspend(ms)   Last(ms)    Min(ms)    Max(ms)
--------------------------------------------------------------------------------------------------------------------------
0000:00:02.0                     active              1        0        45688            0          0          0          0
0000:00:1f.0                     active              1        0        45687            0          0          0          0
0000:00:1f.2                     active              1        0        45686            0          0          0          0
0000:00:1f.3                     suspended           1        1         1658        44028          0          0          0
00:03:0                          active             15       14        19627        25899         42          5      14811
00:03:0.0                        active             14       13        19626        25900         42          5      14811

TESTING:
Tested with an x86_64 defconfig kernel and QEMU.

AI ASSISTANCE:
Gemini was used to prepare this series.

Signed-off-by: Joshua Crofts <crofts@kernel.org>
---
Joshua Crofts (3):
      PM: runtime: add additional suspend/resume metrics
      PM: add sysfs attributes for additional suspend/resume metrics
      PM: runtime: add debugfs entry for pm_runtime_summary

 Documentation/ABI/testing/sysfs-devices-power |  36 ++++++
 drivers/base/power/runtime.c                  | 156 +++++++++++++++++++++++++-
 drivers/base/power/sysfs.c                    |  81 +++++++++++++
 include/linux/pm.h                            |  12 ++
 4 files changed, 281 insertions(+), 4 deletions(-)
---
base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
change-id: 20261110-pm-runtime-summary-8dd29a1383bc

Best regards,
-- 
Joshua Crofts <crofts@kernel.org>

[PATCH 1/3] PM: runtime: add additional suspend/resume metrics

[Joshua Crofts]

The current implementation only logs the total accumulated time a device
spends in suspended or active states.

Add tracking for:
- resume_count : number of successful transitions to active
- suspend_count: number of successful transitions to suspended
- last_suspended_time: duration of the most recent sleep cycle (ns)
- min_suspended_time / max_suspended_sleep: shortest and longest sleep
  cycle durations to help detect power thrashing (ns)

Signed-off-by: Joshua Crofts <crofts@kernel.org>
---
 drivers/base/power/runtime.c | 70 +++++++++++++++++++++++++++++++++++++++++---
 include/linux/pm.h           | 12 ++++++++
 2 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 304a2b12342082ffacce32aa9c2e863466b0d4ae..5087a52f1784f7b4493896bce147ebcb0424d17c 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -5,6 +5,8 @@
  * Copyright (c) 2009 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
  * Copyright (C) 2010 Alan Stern <stern@rowland.harvard.edu>
  */
+#include <linux/pm.h>
+#include <linux/timekeeping.h>
 #include <linux/sched/mm.h>
 #include <linux/ktime.h>
 #include <linux/hrtimer.h>
@@ -103,11 +105,62 @@ static void update_pm_runtime_accounting(struct device *dev)
 		dev->power.active_time += delta;
 }
 
+static void rpm_account_suspend(struct device *dev)
+{
+	dev->power.suspend_time = ktime_get_mono_fast_ns();
+	dev->power.suspend_count++;
+}
+
+static void rpm_account_sleep_end(struct device *dev)
+{
+	u64 now, duration;
+
+	if (!dev->power.suspend_time)
+		return;
+
+	now = ktime_get_mono_fast_ns();
+	if (now <= dev->power.suspend_time)
+		return;
+
+	duration = now - dev->power.suspend_time;
+	dev->power.last_suspended_time = duration;
+
+	/* Update min/max extrema at the exact same moment as last_suspended_time */
+	if (!dev->power.min_suspended_time || duration < dev->power.min_suspended_time)
+		dev->power.min_suspended_time = duration;
+
+	if (duration > dev->power.max_suspended_time)
+		dev->power.max_suspended_time = duration;
+}
+
+static void rpm_account_resume_complete(struct device *dev)
+{
+	dev->power.resume_count++;
+	dev->power.suspend_time = 0;
+}
+
 static void __update_runtime_status(struct device *dev, enum rpm_status status)
 {
+	enum rpm_status old_status = dev->power.runtime_status;
+
 	update_pm_runtime_accounting(dev);
 	trace_rpm_status(dev, status);
 	dev->power.runtime_status = status;
+
+	if (dev->power.disable_depth > 0)
+		return;
+
+	if ((old_status == RPM_SUSPENDING || old_status == RPM_ACTIVE) &&
+	    status == RPM_SUSPENDED)
+		rpm_account_suspend(dev);
+	else if (old_status == RPM_RESUMING && status == RPM_SUSPENDED)
+		dev->power.suspend_time = ktime_get_mono_fast_ns();
+	else if (old_status == RPM_SUSPENDED && status != RPM_SUSPENDED)
+		rpm_account_sleep_end(dev);
+
+	if ((old_status == RPM_RESUMING || old_status == RPM_SUSPENDED) &&
+	    status == RPM_ACTIVE)
+		rpm_account_resume_complete(dev);
 }
 
 static u64 rpm_get_accounted_time(struct device *dev, bool suspended)
@@ -1589,10 +1642,12 @@ void pm_runtime_enable(struct device *dev)
 	dev->power.last_status = RPM_INVALID;
 	dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
 
-	if (dev->power.runtime_status == RPM_SUSPENDED &&
-	    !dev->power.ignore_children &&
-	    atomic_read(&dev->power.child_count) > 0)
-		dev_warn(dev, "Enabling runtime PM for inactive device with active children\n");
+	if (dev->power.runtime_status == RPM_SUSPENDED) {
+		dev->power.suspend_time = dev->power.accounting_timestamp;
+		if (!dev->power.ignore_children &&
+		    atomic_read(&dev->power.child_count) > 0)
+			dev_warn(dev, "Enabling runtime PM for inactive device with active children\n");
+	}
 
 out:
 	spin_unlock_irqrestore(&dev->power.lock, flags);
@@ -1861,6 +1916,13 @@ void pm_runtime_init(struct device *dev)
 	pm_suspend_ignore_children(dev, false);
 	dev->power.runtime_auto = true;
 
+	dev->power.resume_count = 0;
+	dev->power.suspend_count = 0;
+	dev->power.suspend_time = 0;
+	dev->power.last_suspended_time = 0;
+	dev->power.min_suspended_time = 0;
+	dev->power.max_suspended_time = 0;
+
 	dev->power.request_pending = false;
 	dev->power.request = RPM_REQ_NONE;
 	dev->power.deferred_resume = false;
diff --git a/include/linux/pm.h b/include/linux/pm.h
index ef3f1310e749c34d4aff75a2fd7e95b9f2ef3a10..7cd1350ea327be4e800175c2fc0e3b3e35c3ea57 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -747,6 +747,12 @@ struct pm_subsys_data {
  *   state.
  * @accounting_timestamp: Timestamp in nanoseconds of the last runtime PM state
  *   accounting update.
+ * @resume_count: Number of transitions from suspended -> active
+ * @suspend_count: Number of transitions from active -> suspended
+ * @suspend_time: Timestamp when device entered RPM_SUSPENDED
+ * @last_suspended_time: Residency of the last sleep period (ns)
+ * @min_suspended_time: Shortest sleep duration
+ * @max_suspended_time: Longest sleep duration
  * @subsys_data: Subsystem-specific power management data.
  * @set_latency_tolerance: Callback for setting latency tolerance.
  * @qos: Per-device PM Quality of Service (QoS) constraints.
@@ -816,6 +822,12 @@ struct dev_pm_info {
 	u64			active_time;
 	u64			suspended_time;
 	u64			accounting_timestamp;
+	u64			resume_count;
+	u64			suspend_count;
+	u64			suspend_time;
+	u64			last_suspended_time;
+	u64			min_suspended_time;
+	u64			max_suspended_time;
 #endif
 	struct pm_subsys_data	*subsys_data;  /* Owned by the subsystem. */
 	void (*set_latency_tolerance)(struct device *, s32);

-- 
2.47.3

[PATCH 2/3] PM: add sysfs attributes for additional suspend/resume metrics

[Joshua Crofts]

Add sysfs entries for additional suspend/resume statistics. These are
useful for investigating the behaviour of devices with PM runtime
enabled.

Signed-off-by: Joshua Crofts <crofts@kernel.org>
---
 Documentation/ABI/testing/sysfs-devices-power | 36 ++++++++++++
 drivers/base/power/sysfs.c                    | 81 +++++++++++++++++++++++++++
 2 files changed, 117 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
index 9bf7c8a267c58703a8a097ada1f12271271dbe98..03e5783d737120f98a1c88e5e53f56fe176484e5 100644
--- a/Documentation/ABI/testing/sysfs-devices-power
+++ b/Documentation/ABI/testing/sysfs-devices-power
@@ -284,6 +284,42 @@ Description:
 		Reports total time that the device has been suspended, in
 		milliseconds. Used for runtime PM statistics.
 
+What:           /sys/devices/.../power/runtime_resume_count
+Date:           Nov 2026
+Contact:        Joshua Crofts <crofts@kernel.org>
+Description:
+                Reports the total number of times the device entered a resume
+                state.
+
+What:           /sys/devices/.../power/runtime_suspend_count
+Date:           Nov 2026
+Contact:        Joshua Crofts <crofts@kernel.org>
+Description:
+                Reports the total number of times the device entered a suspended
+                state.
+
+What:           /sys/devices/.../power/runtime_last_suspended_time
+Date:           Nov 2026
+Contact:        Joshua Crofts <crofts@kernel.org>
+Description:
+                Reports the residency duration of the most recent suspended
+                state, in milliseconds.
+
+What:           /sys/devices/.../power/runtime_min_suspended_time
+Date:           Nov 2026
+Contact:        Joshua Crofts <crofts@kernel.org>
+Description:
+                Reports the shortest measured duration the device spent in
+                suspended mode, in milliseconds.
+
+What:           /sys/devices/.../power/runtime_max_suspended_time
+Date:           Nov 2026
+Contact:        Joshua Crofts <crofts@kernel.org>
+Description:
+                Reports the longest measured duration the device spent in
+                suspended mode, in milliseconds.
+
+
 What:		/sys/devices/.../power/runtime_usage
 Date:		Apr 2010
 Contact:	Dominik Brodowski <linux@dominikbrodowski.net>
diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
index 13b31a3adc77c0fe0a5c42fcf9b863dd5bc43088..7e5a186b33222d448b5caacaddbaf9913fe41a98 100644
--- a/drivers/base/power/sysfs.c
+++ b/drivers/base/power/sysfs.c
@@ -178,6 +178,82 @@ static ssize_t runtime_status_show(struct device *dev,
 
 static DEVICE_ATTR_RO(runtime_status);
 
+static ssize_t runtime_resume_count_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	u64 count;
+
+	spin_lock_irq(&dev->power.lock);
+	count = dev->power.resume_count;
+	spin_unlock_irq(&dev->power.lock);
+
+	return sysfs_emit(buf, "%llu\n", count);
+}
+static DEVICE_ATTR_RO(runtime_resume_count);
+
+static ssize_t runtime_suspend_count_show(struct device *dev,
+					  struct device_attribute *attr,
+					  char *buf)
+{
+	u64 count;
+
+	spin_lock_irq(&dev->power.lock);
+	count = dev->power.suspend_count;
+	spin_unlock_irq(&dev->power.lock);
+
+	return sysfs_emit(buf, "%llu\n", count);
+}
+static DEVICE_ATTR_RO(runtime_suspend_count);
+
+static ssize_t runtime_last_suspended_time_show(struct device *dev,
+						struct device_attribute *attr,
+						char *buf)
+{
+	u64 tmp;
+
+	spin_lock_irq(&dev->power.lock);
+	tmp = dev->power.last_suspended_time;
+	spin_unlock_irq(&dev->power.lock);
+
+	do_div(tmp, NSEC_PER_MSEC);
+
+	return sysfs_emit(buf, "%llu\n", tmp);
+}
+static DEVICE_ATTR_RO(runtime_last_suspended_time);
+
+static ssize_t runtime_min_suspended_time_show(struct device *dev,
+					       struct device_attribute *attr,
+					       char *buf)
+{
+	u64 tmp;
+
+	spin_lock_irq(&dev->power.lock);
+	tmp = dev->power.min_suspended_time;
+	spin_unlock_irq(&dev->power.lock);
+
+	do_div(tmp, NSEC_PER_MSEC);
+
+	return sysfs_emit(buf, "%llu\n", tmp);
+}
+static DEVICE_ATTR_RO(runtime_min_suspended_time);
+
+static ssize_t runtime_max_suspended_time_show(struct device *dev,
+					       struct device_attribute *attr,
+					       char *buf)
+{
+	u64 tmp;
+
+	spin_lock_irq(&dev->power.lock);
+	tmp = dev->power.max_suspended_time;
+	spin_unlock_irq(&dev->power.lock);
+
+	do_div(tmp, NSEC_PER_MSEC);
+
+	return sysfs_emit(buf, "%llu\n", tmp);
+}
+static DEVICE_ATTR_RO(runtime_max_suspended_time);
+
 static ssize_t autosuspend_delay_ms_show(struct device *dev,
 					 struct device_attribute *attr,
 					 char *buf)
@@ -649,6 +725,11 @@ static struct attribute *runtime_attrs[] = {
 	&dev_attr_runtime_suspended_time.attr,
 	&dev_attr_runtime_active_time.attr,
 	&dev_attr_autosuspend_delay_ms.attr,
+	&dev_attr_runtime_resume_count.attr,
+	&dev_attr_runtime_suspend_count.attr,
+	&dev_attr_runtime_last_suspended_time.attr,
+	&dev_attr_runtime_min_suspended_time.attr,
+	&dev_attr_runtime_max_suspended_time.attr,
 #ifdef CONFIG_PM_ADVANCED_DEBUG
 	&dev_attr_runtime_usage.attr,
 	&dev_attr_runtime_active_kids.attr,

-- 
2.47.3

[PATCH 3/3] PM: runtime: add debugfs entry for pm_runtime_summary

[Joshua Crofts]

Add a debugfs entry for showing the runtime statistics for devices with
PM runtime enabled.

Signed-off-by: Joshua Crofts <crofts@kernel.org>
---
 drivers/base/power/runtime.c | 86 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 5087a52f1784f7b4493896bce147ebcb0424d17c..f5ea6ba6d20fc4a9a3088e1fcb20b70cd5ebe476 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -14,6 +14,8 @@
 #include <linux/pm_runtime.h>
 #include <linux/pm_wakeirq.h>
 #include <linux/rculist.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
 #include <trace/events/rpm.h>
 
 #include "../base.h"
@@ -2193,3 +2195,87 @@ bool pm_runtime_need_not_resume(struct device *dev)
 }
 
 #endif /* CONFIG_PM_SLEEP */
+
+#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_PM_SLEEP)
+static void rpm_summary_show_dev(struct device *dev, void *data)
+{
+	struct seq_file *s = data;
+	unsigned long flags;
+	u64 active_time, suspended_time;
+	u64 last_sleep, min_sleep, max_sleep;
+	u64 resumes, suspends;
+	const char *status_str;
+	bool enabled;
+
+	spin_lock_irqsave(&dev->power.lock, flags);
+
+	enabled = pm_runtime_enabled(dev);
+	if (!enabled && !dev->power.resume_count && !dev->power.suspend_count) {
+		spin_unlock_irqrestore(&dev->power.lock, flags);
+		return;
+	}
+
+	update_pm_runtime_accounting(dev);
+
+	switch (dev->power.runtime_status) {
+	case RPM_ACTIVE:
+		status_str = "active";
+		break;
+	case RPM_SUSPENDED:
+		status_str = "suspended";
+		break;
+	case RPM_SUSPENDING:
+		status_str = "suspending";
+		break;
+	case RPM_RESUMING:
+		status_str = "resuming";
+		break;
+	default:
+		status_str = "unknown";
+		break;
+	}
+
+	active_time = dev->power.active_time;
+	suspended_time = dev->power.suspended_time;
+	resumes = dev->power.resume_count;
+	suspends = dev->power.suspend_count;
+	last_sleep = dev->power.last_suspended_time;
+	min_sleep = dev->power.min_suspended_time;
+	max_sleep = dev->power.max_suspended_time;
+
+	spin_unlock_irqrestore(&dev->power.lock, flags);
+
+	do_div(active_time, NSEC_PER_MSEC);
+	do_div(suspended_time, NSEC_PER_MSEC);
+	do_div(last_sleep, NSEC_PER_MSEC);
+	do_div(min_sleep, NSEC_PER_MSEC);
+	do_div(max_sleep, NSEC_PER_MSEC);
+
+	seq_printf(s, "%-32s %-12s %8llu %8llu %12llu %12llu %10llu %10llu %10llu\n",
+		   dev_name(dev), enabled ? status_str : "disabled",
+		   resumes, suspends, active_time, suspended_time,
+		   last_sleep, min_sleep, max_sleep);
+}
+
+static int pm_runtime_summary_show(struct seq_file *s, void *unused)
+{
+	seq_printf(s, "%-32s %-12s %8s %8s %12s %12s %10s %10s %10s\n",
+		   "Device", "Status", "Resumes", "Suspends",
+		   "Active(ms)", "Suspend(ms)", "Last(ms)", "Min(ms)", "Max(ms)");
+	seq_puts(s, "--------------------------------------------------------------------------------------------------------------------------\n");
+
+	dpm_for_each_dev(s, rpm_summary_show_dev);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(pm_runtime_summary);
+
+static int __init pm_runtime_debugfs_init(void)
+{
+	debugfs_create_file("pm_runtime_summary", 0444, NULL, NULL,
+			    &pm_runtime_summary_fops);
+
+	return 0;
+}
+late_initcall(pm_runtime_debugfs_init);
+#endif /* defined(CONFIG_DEBUG_FS) && defined(CONFIG_PM_SLEEP) */

-- 
2.47.3