[PATCH v7] PM: sleep: Expose last succeeded resumed timestamp in sysfs

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Expose last succeeded resumed timestamp as last_success_resume_time
attribute of suspend_stats in sysfs so that user can use this time
stamp as a reference point of resuming user space.

On some system like the ChromeOS, the system suspend and resume are
controlled by a power management process. The user-space tasks will be
noticed the suspend and the resume signal from it.
To improve the suspend/resume performance and/or to find regressions,
we would like to know how long the resume processes are taken in kernel
and in user-space.
For this purpose, expose the accarate time when the kernel is finished
to resume so that we can distinguish the duration of kernel resume and
user space resume.

This suspend_stats attribute is easy to access and only expose the
timestamp in CLOCK_MONOTONIC. User can find the accarate time when the
kernel finished to resume its drivers/subsystems and start thawing, and
measure the elapsed time from the time when the kernel finished the
resume to a user-space action (e.g. displaying the UI).

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 Changes in v7:
  - Update patch description.
  - Update sysfs documentation to say the exact timing.
  - Update the comment.
 Changes in v6:
  - Fix to record resume time before thawing user processes.
 Changes in v5:
  - Just updated for v6.7-rc3.
 Changes in v4.1:
  - Fix document typo (again).
 Changes in v4:
  - Update description to add why.
  - Fix document typo.
 Changes in v3:
  - Add (unsigned long long) casting for %llu.
  - Add a line after last_success_resume_time_show().
 Changes in v2:
  - Use %llu instead of %lu for printing u64 value.
  - Remove unneeded indent spaces from the last_success_resume_time
    line in the debugfs suspend_stat file.
---
 Documentation/ABI/testing/sysfs-power |   11 +++++++++++
 include/linux/suspend.h               |    2 ++
 kernel/power/main.c                   |   15 +++++++++++++++
 kernel/power/suspend.c                |    9 +++++++++
 4 files changed, 37 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index a3942b1036e2..ee567e7e9d4a 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -442,6 +442,17 @@ Description:
 		'total_hw_sleep' and 'last_hw_sleep' may not be accurate.
 		This number is measured in microseconds.
 
+What:		/sys/power/suspend_stats/last_success_resume_time
+Date:		Dec 2023
+Contact:	Masami Hiramatsu <mhiramat@xxxxxxxxxx>
+Description:
+		The /sys/power/suspend_stats/last_success_resume_time file
+		contains the timestamp of when the kernel successfully
+		resumed drivers/subsystems from suspend/hibernate. This is
+		just before thawing the user processes.
+		This floating point number is measured in seconds by monotonic
+		clock.
+
 What:		/sys/power/sync_on_suspend
 Date:		October 2019
 Contact:	Jonas Meurer <jonas@xxxxxxxxxxxxxxx>
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index ef503088942d..ddd789044960 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -8,6 +8,7 @@
 #include <linux/pm.h>
 #include <linux/mm.h>
 #include <linux/freezer.h>
+#include <linux/timekeeping.h>
 #include <asm/errno.h>
 
 #ifdef CONFIG_VT
@@ -71,6 +72,7 @@ struct suspend_stats {
 	u64	last_hw_sleep;
 	u64	total_hw_sleep;
 	u64	max_hw_sleep;
+	struct timespec64 last_success_resume_time;
 	enum suspend_stat_step	failed_steps[REC_FAILED_NUM];
 };
 
diff --git a/kernel/power/main.c b/kernel/power/main.c
index f6425ae3e8b0..2ab23fd3daac 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -421,6 +421,17 @@ static ssize_t last_failed_step_show(struct kobject *kobj,
 }
 static struct kobj_attribute last_failed_step = __ATTR_RO(last_failed_step);
 
+static ssize_t last_success_resume_time_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%llu.%llu\n",
+		(unsigned long long)suspend_stats.last_success_resume_time.tv_sec,
+		(unsigned long long)suspend_stats.last_success_resume_time.tv_nsec);
+}
+
+static struct kobj_attribute last_success_resume_time =
+			__ATTR_RO(last_success_resume_time);
+
 static struct attribute *suspend_attrs[] = {
 	&success.attr,
 	&fail.attr,
@@ -438,6 +449,7 @@ static struct attribute *suspend_attrs[] = {
 	&last_hw_sleep.attr,
 	&total_hw_sleep.attr,
 	&max_hw_sleep.attr,
+	&last_success_resume_time.attr,
 	NULL,
 };
 
@@ -514,6 +526,9 @@ static int suspend_stats_show(struct seq_file *s, void *unused)
 			suspend_step_name(
 				suspend_stats.failed_steps[index]));
 	}
+	seq_printf(s,	"last_success_resume_time:\t%-llu.%llu\n",
+		   (unsigned long long)suspend_stats.last_success_resume_time.tv_sec,
+		   (unsigned long long)suspend_stats.last_success_resume_time.tv_nsec);
 
 	return 0;
 }
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index fa3bf161d13f..2d0f46b4d0cf 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -595,6 +595,15 @@ static int enter_state(suspend_state_t state)
  Finish:
 	events_check_enabled = false;
 	pm_pr_dbg("Finishing wakeup.\n");
+
+	/*
+	 * Record last succeeded resume timestamp just before thawing processes.
+	 * This is for helping users to measure user-space resume performance
+	 * for improving their programs or finding regressions.
+	 */
+	if (!error)
+		ktime_get_ts64(&suspend_stats.last_success_resume_time);
+
 	suspend_finish();
  Unlock:
 	mutex_unlock(&system_transition_mutex);