[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@xxxxxxxxxx>
---
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@xxxxxxxxxx>