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

["Limonciello, Mario" <mario.limonciello@amd.com>]

On 3/31/2023 13:01, Rafael J. Wysocki wrote:
> 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?

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@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".

Ack, thanks.

> 
>> +               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;
> 

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
>> --