linux-kernel - Re: [PATCH v8 0/1] PM: sleep: Expose last succeeded resumed timestamp in sysfs

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Message-Id: <20240709085005.8a348fdfed6afcb8635aea11@kernel.org>
Date: Tue, 9 Jul 2024 08:50:05 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.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>, Randy Dunlap <rdunlap@...radead.org>,
 suleiman@...gle.com, briannorris@...gle.com, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org
Subject: Re: [PATCH v8 0/1] PM: sleep: Expose last succeeded resumed
 timestamp in sysfs

Hi Rafael,

Gentry ping. I would like to hear your comment on it.

Thank you,

On Tue,  2 Jul 2024 23:24:43 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> Hi,
> 
> Here is the 8th version of the patch to expose last succeeded resumed
> timestamp in sysfs as /sys/power/suspend_stats/last_success_resume_time.
> The previous version is here.
> 
> https://lore.kernel.org/lkml/170359668692.1864392.6909734045167510522.stgit@mhiramat.roam.corp.google.com/
> 
> This version is just update against for the upstream kernel.
> 
> 
> On some system like the ChromeOS, the system suspend and resume are
> controlled by a power management process. The user-space tasks will be
> noticed the suspend and the resume signal from it.
> To improve the suspend/resume performance and/or to find regressions,
> we would like to know how long the resume processes are taken in kernel
> and in user-space.
> 
> This patch introduces a last succeeded resumed timestamp (just before
> thawing processes) on sysfs which allows us to find when the kernel
> resume process successfully done in MONOTONIC clock. Thus user processes
> can measure the elapsed time taken by its resume process at any point
> in time.
> 
> This will help us to detect abnormal value (longer time) process in
> the resuming and quickly decide the root cause is in the kernel or
> user-space. The kernel side we can use many tools (e.g. printk or
> ftrace) but for user-space we need to define the starting point of
> the resuming process. Actually, the kernel side needs to use local
> clock because the clock subsystem is also suspended. But in that
> case, user space can not use that timestamp because the local clock
> is not exposed.
> 
> So this will be used something like
> 
> where_the_user_space_resume_finish() {
> 	clock_gettime(CLOCK_MONOTONIC, &etime_ts);
> 	fileread("/sys/.../last_success_resume_time", stime);
> 	convert_timespec(stime, &stime_ts);
> 	user_resume_time = timespec_delta(&etime_ts, &stime_ts);
> 	...
> }
> 
> Thank you,
> 
> ---
> 
> Masami Hiramatsu (1):
>       PM: sleep: Expose last succeeded resumed timestamp in sysfs
> 
> 
>  Documentation/ABI/testing/sysfs-power |   11 +++++++++++
>  kernel/power/main.c                   |   28 ++++++++++++++++++++++++++++
>  kernel/power/power.h                  |    1 +
>  kernel/power/suspend.c                |    1 +
>  4 files changed, 41 insertions(+)
> 
> --
> Masami Hiramatsu (Google) <mhiramat@...nel.org>


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