RE: [PATCH v7 1/4] PM: Add sysfs files to represent time spent in hardware sleep state

[Limonciello, Mario]

[Public]

> 
> On 4/11/23 23:17, Mario Limonciello 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 two new sysfs files:
> > 1) The time spent in a hw sleep state for last cycle.
> > 2) The time spent in a hw sleep state since the kernel booted
> > Both of these files will be present only if the system supports s2idle.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> > v6->v7:
> >  * Rename to max_hw_sleep (David E Box)
> >  * Drop overflow checks (David E Box)
> > v5->v6:
> >  * Add total attribute as well
> >  * Change text for documentation
> >  * Adjust flow of is_visible callback.
> >  * If overflow was detected in total attribute return -EOVERFLOW
> >  * Rename symbol
> >  * Add stub for symbol for builds without CONFIG_PM_SLEEP
> > v4->v5:
> >  * Provide time in microseconds instead of percent. Userspace can convert
> >    this if desirable.
> > ---
> >  Documentation/ABI/testing/sysfs-power | 24 ++++++++++++++++
> >  include/linux/suspend.h               |  5 ++++
> >  kernel/power/main.c                   | 40 +++++++++++++++++++++++++++
> >  3 files changed, 69 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-power
> b/Documentation/ABI/testing/sysfs-power
> > index f99d433ff311..0723b4dadfbe 100644
> > --- a/Documentation/ABI/testing/sysfs-power
> > +++ b/Documentation/ABI/testing/sysfs-power
> > @@ -413,6 +413,30 @@ 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 in the most recent system suspend-resume cycle.
> > +		This number is measured in microseconds.
> > +
> > +		NOTE: Limitations in the size of the hardware counters may
> > +		cause this value to be inaccurate in longer sleep cycles.
> 
> Hmm I thought that the plan was to add a separate sysfs attr with
> the max time that the hw could represent here, so that userspace
> actually know what constitutes a "longer sleep cycle" ?
> 
> That would seem better then such a handwavy comment in the ABI docs?

I obviously misunderstood what you were suggesting.
I don't believe we have a way to programmatically determine what the hardware
Internally uses for it's counter to know this.

So it would need to be a table of some sorts that a given system can support
such value.  If we do that, we can actually know whether to return an error code
like -EOVERFLOW or -EINVAL too if the suspend was too long.

I would need Intel guys to share this information though which systems have
which size of counters to make this happen.

> 
> > +
> > +What:		/sys/power/suspend_stats/max_hw_sleep
> > +Date:		June 2023
> > +Contact:	Mario Limonciello <mario.limonciello@xxxxxxx>
> > +Description:
> > +		The /sys/power/suspend_stats/max_hw_sleep file
> > +		contains the aggregate of time spent in a hardware sleep
> > +		state since the kernel was booted. This number
> > +		is measured in microseconds.
> > +
> > +		NOTE: Limitations in the size of the hardware counters may
> > +		cause this value to be inaccurate in longer sleep cycles.
> 
> Maybe "total_hw_sleep" instead of "max_hw_sleep" ? Also since max to
> me sounds like the limit of the longest sleep the hw counters can
> register, so that is bit confusing with the discussion about those
> limits.

total_hw_sleep is actually what was in v6 and max_hw_sleep is what suggested.
That's why I got confused about what you guys meant.

> 
> Regards,
> 
> Hans
> 
> 
> 
> > +
> >  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..819e9677fd10 100644
> > --- a/include/linux/suspend.h
> > +++ b/include/linux/suspend.h
> > @@ -68,6 +68,8 @@ struct suspend_stats {
> >  	int	last_failed_errno;
> >  	int	errno[REC_FAILED_NUM];
> >  	int	last_failed_step;
> > +	u64	last_hw_sleep;
> > +	u64	max_hw_sleep;
> >  	enum suspend_stat_step	failed_steps[REC_FAILED_NUM];
> >  };
> >
> > @@ -489,6 +491,7 @@ 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_report_hw_sleep_time(u64 t);
> >
> >  #define pm_notifier(fn, pri) {				\
> >  	static struct notifier_block fn##_nb =			\
> > @@ -526,6 +529,8 @@ static inline int unregister_pm_notifier(struct
> notifier_block *nb)
> >  	return 0;
> >  }
> >
> > +static inline void pm_report_hw_sleep_time(u64 t) {};
> > +
> >  static inline void ksys_sync_helper(void) {}
> >
> >  #define pm_notifier(fn, pri)	do { (void)(fn); } while (0)
> > diff --git a/kernel/power/main.c b/kernel/power/main.c
> > index 31ec4a9b9d70..a5546b91ecc9 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 +84,13 @@ int unregister_pm_notifier(struct notifier_block *nb)
> >  }
> >  EXPORT_SYMBOL_GPL(unregister_pm_notifier);
> >
> > +void pm_report_hw_sleep_time(u64 t)
> > +{
> > +	suspend_stats.last_hw_sleep = t;
> > +	suspend_stats.max_hw_sleep += t;
> > +}
> > +EXPORT_SYMBOL_GPL(pm_report_hw_sleep_time);
> > +
> >  int pm_notifier_call_chain_robust(unsigned long val_up, unsigned long
> val_down)
> >  {
> >  	int ret;
> > @@ -377,6 +385,22 @@ 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 ssize_t max_hw_sleep_show(struct kobject *kobj,
> > +		struct kobj_attribute *attr, char *buf)
> > +{
> > +	if (suspend_stats.max_hw_sleep == -EOVERFLOW)
> > +		return suspend_stats.max_hw_sleep;
> > +	return sysfs_emit(buf, "%llu\n", suspend_stats.max_hw_sleep);
> > +}
> > +static struct kobj_attribute max_hw_sleep =
> __ATTR_RO(max_hw_sleep);
> > +
> >  static struct attribute *suspend_attrs[] = {
> >  	&success.attr,
> >  	&fail.attr,
> > @@ -391,12 +415,28 @@ static struct attribute *suspend_attrs[] = {
> >  	&last_failed_dev.attr,
> >  	&last_failed_errno.attr,
> >  	&last_failed_step.attr,
> > +	&last_hw_sleep.attr,
> > +	&max_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 &&
> > +	    attr != &max_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