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

[Limonciello, Mario]

On 3/31/2023 13:01, Rafael J. Wysocki wrote:
> On Thu, Mar 30, 2023 at 9:45 PM Mario Limonciello
> <mario.limonciello@xxxxxxx> 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?

Yes; that's correct.

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

I had considered this; but I didn't think it was actually very useful 
because userspace will get control at the end of every cycle and can 
accumulate those numbers if desirable.

> > This file will be present only if the system supports s2idle.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> > 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@xxxxxxx>
> > +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".

Ack, thanks.

> > +               is measured in microseconds.
> > +
> >   What:          /sys/power/sync_on_suspend
> >   Date:          October 2019
> >   Contact:       Jonas Meurer <jonas@xxxxxxxxxxxxxxx>
> > 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;

Ack, thanks.

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