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

[Samuel Wu]

On Tue, Nov 10, 2026 at 3:34 AM Joshua Crofts <crofts@xxxxxxxxxx> wrote:
>
> 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>

What is the vision for using these runtime PM stats once surfaced to
userspace? Runtime PM and suspend have disjoint portions, but I'm
curious if you see any non-obvious areas where these stats would be
insightful.

And is there a reason the stats need to be surfaced in both sysfs and debugfs?

Thanks!
Sam