Re: [PATCH v7] PM: sleep: Expose last succeeded resumed timestamp in sysfs

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Gently ping,

I would like to know this is enough or I should add more info/update.

Thank you,

On Tue, 26 Dec 2023 22:18:16 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu <mhiramat@kernel.org>
> 
> Expose last succeeded resumed timestamp as last_success_resume_time
> attribute of suspend_stats in sysfs so that user can use this time
> stamp as a reference point of resuming user space.
> 
> 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.
> For this purpose, expose the accarate time when the kernel is finished
> to resume so that we can distinguish the duration of kernel resume and
> user space resume.
> 
> This suspend_stats attribute is easy to access and only expose the
> timestamp in CLOCK_MONOTONIC. User can find the accarate time when the
> kernel finished to resume its drivers/subsystems and start thawing, and
> measure the elapsed time from the time when the kernel finished the
> resume to a user-space action (e.g. displaying the UI).
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  Changes in v7:
>   - Update patch description.
>   - Update sysfs documentation to say the exact timing.
>   - Update the comment.
>  Changes in v6:
>   - Fix to record resume time before thawing user processes.
>  Changes in v5:
>   - Just updated for v6.7-rc3.
>  Changes in v4.1:
>   - Fix document typo (again).
>  Changes in v4:
>   - Update description to add why.
>   - Fix document typo.
>  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 |   11 +++++++++++
>  include/linux/suspend.h               |    2 ++
>  kernel/power/main.c                   |   15 +++++++++++++++
>  kernel/power/suspend.c                |    9 +++++++++
>  4 files changed, 37 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
> index a3942b1036e2..ee567e7e9d4a 100644
> --- a/Documentation/ABI/testing/sysfs-power
> +++ b/Documentation/ABI/testing/sysfs-power
> @@ -442,6 +442,17 @@ 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:		Dec 2023
> +Contact:	Masami Hiramatsu <mhiramat@kernel.org>
> +Description:
> +		The /sys/power/suspend_stats/last_success_resume_time file
> +		contains the timestamp of when the kernel successfully
> +		resumed drivers/subsystems from suspend/hibernate. This is
> +		just before thawing the user processes.
> +		This floating point number is measured in seconds by monotonic
> +		clock.
> +
>  What:		/sys/power/sync_on_suspend
>  Date:		October 2019
>  Contact:	Jonas Meurer <jonas@freesources.org>
> diff --git a/include/linux/suspend.h b/include/linux/suspend.h
> index ef503088942d..ddd789044960 100644
> --- a/include/linux/suspend.h
> +++ b/include/linux/suspend.h
> @@ -8,6 +8,7 @@
>  #include <linux/pm.h>
>  #include <linux/mm.h>
>  #include <linux/freezer.h>
> +#include <linux/timekeeping.h>
>  #include <asm/errno.h>
>  
>  #ifdef CONFIG_VT
> @@ -71,6 +72,7 @@ struct suspend_stats {
>  	u64	last_hw_sleep;
>  	u64	total_hw_sleep;
>  	u64	max_hw_sleep;
> +	struct timespec64 last_success_resume_time;
>  	enum suspend_stat_step	failed_steps[REC_FAILED_NUM];
>  };
>  
> diff --git a/kernel/power/main.c b/kernel/power/main.c
> index f6425ae3e8b0..2ab23fd3daac 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -421,6 +421,17 @@ static ssize_t last_failed_step_show(struct kobject *kobj,
>  }
>  static struct kobj_attribute last_failed_step = __ATTR_RO(last_failed_step);
>  
> +static ssize_t last_success_resume_time_show(struct kobject *kobj,
> +		struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%llu.%llu\n",
> +		(unsigned long long)suspend_stats.last_success_resume_time.tv_sec,
> +		(unsigned long long)suspend_stats.last_success_resume_time.tv_nsec);
> +}
> +
> +static struct kobj_attribute last_success_resume_time =
> +			__ATTR_RO(last_success_resume_time);
> +
>  static struct attribute *suspend_attrs[] = {
>  	&success.attr,
>  	&fail.attr,
> @@ -438,6 +449,7 @@ static struct attribute *suspend_attrs[] = {
>  	&last_hw_sleep.attr,
>  	&total_hw_sleep.attr,
>  	&max_hw_sleep.attr,
> +	&last_success_resume_time.attr,
>  	NULL,
>  };
>  
> @@ -514,6 +526,9 @@ static int suspend_stats_show(struct seq_file *s, void *unused)
>  			suspend_step_name(
>  				suspend_stats.failed_steps[index]));
>  	}
> +	seq_printf(s,	"last_success_resume_time:\t%-llu.%llu\n",
> +		   (unsigned long long)suspend_stats.last_success_resume_time.tv_sec,
> +		   (unsigned long long)suspend_stats.last_success_resume_time.tv_nsec);
>  
>  	return 0;
>  }
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index fa3bf161d13f..2d0f46b4d0cf 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -595,6 +595,15 @@ static int enter_state(suspend_state_t state)
>   Finish:
>  	events_check_enabled = false;
>  	pm_pr_dbg("Finishing wakeup.\n");
> +
> +	/*
> +	 * Record last succeeded resume timestamp just before thawing processes.
> +	 * This is for helping users to measure user-space resume performance
> +	 * for improving their programs or finding regressions.
> +	 */
> +	if (!error)
> +		ktime_get_ts64(&suspend_stats.last_success_resume_time);
> +
>  	suspend_finish();
>   Unlock:
>  	mutex_unlock(&system_transition_mutex);
> 


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