linux-kernel - [PATCH v6 0/1] PM: sleep: Expose last succeeded resumed timestamp in sysfs

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Message-ID:  <170245316678.651355.6640896026073025688.stgit@mhiramat.roam.corp.google.com>
Date:   Wed, 13 Dec 2023 16:39:26 +0900
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>
Cc:     suleiman@...gle.com, briannorris@...gle.com,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: [PATCH v6 0/1] PM: sleep: Expose last succeeded resumed timestamp in sysfs

Hi,

Here is the 6th 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/all/170108151076.780347.2482745314490930894.stgit@mhiramat.roam.corp.google.com/

This version fixes the timestamp recording timing to right before thawing
user processes and is rebased on v6.7-rc5. 

This allows us to find when the kernel resume process successfully done
in the sysfs 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 |   10 ++++++++++
 include/linux/suspend.h               |    2 ++
 kernel/power/main.c                   |   15 +++++++++++++++
 kernel/power/suspend.c                |    3 +++
 4 files changed, 30 insertions(+)

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