Re: [PATCH v5 1/4] PM: Add a sysfs file to represent time spent in hardware sleep state

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, Mar 30, 2023 at 9:45 PM Mario Limonciello
<mario.limonciello@amd.com> wrote:
>
> Userspace can't easily discover how much of a sleep cycle was spent in a
> hardware sleep state without using kernel tracing and vendor specific sysfs
> or debugfs files.
>
> To make this information more discoverable, introduce a new sysfs file
> to represent the time spent in a sleep state.

This is only in the most recent suspend-resume cycle, isn't it?

Wouldn't it be useful to have another attribute printing the
accumulated total HW sleep time?

> This file will be present only if the system supports s2idle.
>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> v4->v5:
>  * Provide time in microseconds instead of percent. Userspace can convert
>    this if desirable.
> ---
>  Documentation/ABI/testing/sysfs-power |  9 +++++++++
>  include/linux/suspend.h               |  2 ++
>  kernel/power/main.c                   | 29 +++++++++++++++++++++++++++
>  3 files changed, 40 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
> index f99d433ff311..9e0c31b9ce85 100644
> --- a/Documentation/ABI/testing/sysfs-power
> +++ b/Documentation/ABI/testing/sysfs-power
> @@ -413,6 +413,15 @@ Description:
>                 The /sys/power/suspend_stats/last_failed_step file contains
>                 the last failed step in the suspend/resume path.
>
> +What:          /sys/power/suspend_stats/last_hw_sleep
> +Date:          June 2023
> +Contact:       Mario Limonciello <mario.limonciello@amd.com>
> +Description:
> +               The /sys/power/suspend_stats/last_hw_sleep file
> +               contains the duration of time spent in a hardware sleep
> +               state during from the previous suspend cycle. This number

"during from"?

I would say "in the most recent system suspend-resume cycle".

> +               is measured in microseconds.
> +
>  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 cfe19a028918..e0f2ac5f4406 100644
> --- a/include/linux/suspend.h
> +++ b/include/linux/suspend.h
> @@ -68,6 +68,7 @@ struct suspend_stats {
>         int     last_failed_errno;
>         int     errno[REC_FAILED_NUM];
>         int     last_failed_step;
> +       u64     last_hw_sleep;
>         enum suspend_stat_step  failed_steps[REC_FAILED_NUM];
>  };
>
> @@ -489,6 +490,7 @@ void restore_processor_state(void);
>  extern int register_pm_notifier(struct notifier_block *nb);
>  extern int unregister_pm_notifier(struct notifier_block *nb);
>  extern void ksys_sync_helper(void);
> +extern void pm_set_hw_sleep_time(u64 t);
>
>  #define pm_notifier(fn, pri) {                         \
>         static struct notifier_block fn##_nb =                  \
> diff --git a/kernel/power/main.c b/kernel/power/main.c
> index 31ec4a9b9d70..6a2bf8784ce8 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -6,6 +6,7 @@
>   * Copyright (c) 2003 Open Source Development Lab
>   */
>
> +#include <linux/acpi.h>
>  #include <linux/export.h>
>  #include <linux/kobject.h>
>  #include <linux/string.h>
> @@ -83,6 +84,12 @@ int unregister_pm_notifier(struct notifier_block *nb)
>  }
>  EXPORT_SYMBOL_GPL(unregister_pm_notifier);
>
> +void pm_set_hw_sleep_time(u64 t)
> +{
> +       suspend_stats.last_hw_sleep = t;
> +}
> +EXPORT_SYMBOL_GPL(pm_set_hw_sleep_time);
> +
>  int pm_notifier_call_chain_robust(unsigned long val_up, unsigned long val_down)
>  {
>         int ret;
> @@ -377,6 +384,13 @@ 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_hw_sleep_show(struct kobject *kobj,
> +               struct kobj_attribute *attr, char *buf)
> +{
> +       return sysfs_emit(buf, "%llu\n", suspend_stats.last_hw_sleep);
> +}
> +static struct kobj_attribute last_hw_sleep = __ATTR_RO(last_hw_sleep);
> +
>  static struct attribute *suspend_attrs[] = {
>         &success.attr,
>         &fail.attr,
> @@ -391,12 +405,27 @@ static struct attribute *suspend_attrs[] = {
>         &last_failed_dev.attr,
>         &last_failed_errno.attr,
>         &last_failed_step.attr,
> +       &last_hw_sleep.attr,
>         NULL,
>  };
>
> +static umode_t suspend_attr_is_visible(struct kobject *kobj, struct attribute *attr, int idx)
> +{
> +       if (attr == &last_hw_sleep.attr) {
> +#ifdef CONFIG_ACPI
> +               if (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)
> +                       return 0444;
> +#endif
> +               return 0;
> +       }
> +
> +       return 0444;

if (attr != &last_hw_sleep.attr)
        return 0444;

#ifdef CONFIG_ACPI
if (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)
        return 0444;
#endif

return 0;

> +}
> +
>  static const struct attribute_group suspend_attr_group = {
>         .name = "suspend_stats",
>         .attrs = suspend_attrs,
> +       .is_visible = suspend_attr_is_visible,
>  };
>
>  #ifdef CONFIG_DEBUG_FS
> --