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

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Date:   Sun, 29 Oct 2023 05:16:49 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        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 19:54, Masami Hiramatsu (Google) wrote:
> On Sat, 28 Oct 2023 09:48:36 -0700
> Randy Dunlap <rdunlap@...radead.org> wrote:
> 
>> 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?

and what about this part of my questions? ^^^^^^^^^


>>
>>>
>>> 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...
> 
> Oops, it should be "floating point number".
> 
> Thank you!
> 
>>
>>
>>> +		clock.
>>> +
>>>  What:		/sys/power/sync_on_suspend
>>>  Date:		October 2019
>>>  Contact:	Jonas Meurer <jonas@...esources.org>
>>
>> [snip]
>>
>> Thanks.
>> -- 
>> ~Randy
> 
> 

-- 
~Randy