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

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Message-Id: <20231029115449.8c942b131312c2464eda6970@kernel.org>
Date:   Sun, 29 Oct 2023 11:54:49 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Randy Dunlap <rdunlap@...radead.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

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?
> 
> > 
> > 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


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>