linux-kernel - Re: [PATCH v3] PM: sleep: Expose last succeeded resumed timestamp in sysfs

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Date:   Sat, 28 Oct 2023 09:48:36 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>
Cc:     suleiman@...gle.com, briannorris@...gle.com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3] PM: sleep: Expose last succeeded resumed timestamp in
 sysfs

Hi,

On 10/28/23 05:53, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu <mhiramat@...nel.org>
> 
> Expose last succeeded resumed timestamp as last_success_resume_time
> attribute of suspend_stats in sysfs. This timestamp is recorded in
> CLOCK_MONOTONIC. So user can find the actual resumed time and
> measure the elapsed time from the time when the kernel finished
> the resume to the user-space action (e.g. display the UI).

Can you go into the use-case a bit more, please?
You have said "what", but not "why".
What do you (or google) plan to do with this?

> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
>  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 |   10 ++++++++++
>  include/linux/suspend.h               |    2 ++
>  kernel/power/main.c                   |   15 +++++++++++++++
>  kernel/power/suspend.c                |    1 +
>  4 files changed, 28 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
> index a3942b1036e2..63659765dee1 100644
> --- a/Documentation/ABI/testing/sysfs-power
> +++ b/Documentation/ABI/testing/sysfs-power
> @@ -442,6 +442,16 @@ 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:		Oct 2023
> +Contact:	Masami Hiramatsu <mhiramat@...nel.org>
> +Description:
> +		The /sys/power/suspend_stats/last_success_resume_time file
> +		contains the timestamp of when the kernel successfully
> +		resumed from suspend/hibernate.
> +		This floating number is measured in seconds by monotonic

What does "floating" mean here?  Not floating point...


> +		clock.
> +
>  What:		/sys/power/sync_on_suspend
>  Date:		October 2019
>  Contact:	Jonas Meurer <jonas@...esources.org>

[snip]

Thanks.
-- 
~Randy