In resume_store(), if the device number written to /sys/power/resume
is the same as the current swsusp_resume_device, we can skip reassignment.
This avoids unnecessary locking and improves efficiency slightly.

Signed-off-by: Zihuan Zhang <zhangzihuan@kylinos.cn>
---
 kernel/power/hibernate.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 519fb09de5e0..504a1c2465ce 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -1291,6 +1291,9 @@ static ssize_t resume_store(struct kobject *kobj, struct kobj_attribute *attr,
 	if (error)
 		return error;
 
+	if (dev == swsusp_resume_device)
+		return n;
+
 	sleep_flags = lock_system_sleep();
 	swsusp_resume_device = dev;
 	unlock_system_sleep(sleep_flags);
-- 
2.25.1

On Fri, May 30, 2025 at 12:00 PM Zihuan Zhang <zhangzihuan@kylinos.cn> wrote:
>
> In resume_store(), if the device number written to /sys/power/resume
> is the same as the current swsusp_resume_device, we can skip reassignment.
> This avoids unnecessary locking and improves efficiency slightly.
>
> Signed-off-by: Zihuan Zhang <zhangzihuan@kylinos.cn>
> ---
>  kernel/power/hibernate.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index 519fb09de5e0..504a1c2465ce 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1291,6 +1291,9 @@ static ssize_t resume_store(struct kobject *kobj, struct kobj_attribute *attr,
>         if (error)
>                 return error;
>
> +       if (dev == swsusp_resume_device)
> +               return n;
> +

The main purpose of this function is to run software_resume(), not to
set swsusp_resume_device.  You're breaking it with this change.

>         sleep_flags = lock_system_sleep();
>         swsusp_resume_device = dev;
>         unlock_system_sleep(sleep_flags);
> --
> 2.25.1
>

Hi Rafael,

在 2025/7/3 02:51, Rafael J. Wysocki 写道:
> On Fri, May 30, 2025 at 12:00 PM Zihuan Zhang <zhangzihuan@kylinos.cn> wrote:
>> In resume_store(), if the device number written to /sys/power/resume
>> is the same as the current swsusp_resume_device, we can skip reassignment.
>> This avoids unnecessary locking and improves efficiency slightly.
>>
>> Signed-off-by: Zihuan Zhang <zhangzihuan@kylinos.cn>
>> ---
>>   kernel/power/hibernate.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index 519fb09de5e0..504a1c2465ce 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -1291,6 +1291,9 @@ static ssize_t resume_store(struct kobject *kobj, struct kobj_attribute *attr,
>>          if (error)
>>                  return error;
>>
>> +       if (dev == swsusp_resume_device)
>> +               return n;
>> +
> The main purpose of this function is to run software_resume(), not to
> set swsusp_resume_device.  You're breaking it with this change.
Thank you for the feedback.

You’re absolutely right — I misunderstood the primary role of 
resume_store() as being only to update swsusp_resume_device, and I 
overlooked that its main purpose is to trigger software_resume().

I’ll drop this patch accordingly. Thanks again for pointing this out.

>>          sleep_flags = lock_system_sleep();
>>          swsusp_resume_device = dev;
>>          unlock_system_sleep(sleep_flags);
>> --
>> 2.25.1
>>
Best regards,
Zihuan Zhang