linux-kernel - Re: [PATCH V4] suspend: enable freeze timeout configuration through sys

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Date:	Sun, 03 Feb 2013 14:41:27 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	fli24 <fei.li@...el.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, chuansheng.liu@...el.com
Subject: Re: [PATCH V4] suspend: enable freeze timeout configuration through sys

On Friday, February 01, 2013 04:56:03 PM fli24 wrote:

The code looks OK, but I'm still having a more fundamental problem with this
change, because ->

> At present, the value of timeout for freezing is 20s, which is
> meaningless in case that one thread is frozen with mutex locked
> and another thread is trying to lock the mutex, as this time of
> freezing will fail unavoidably.

-> the situation described above shouldn't happen and if it does, then there
is a bug that needs to be fixed.

The change you're proposing seems to be targeted at hiding those bugs rather
than at fixing them.  I wonder why we should hide those bugs instead of fixing
them?

Rafael


> And if there is no new wakeup event registered, the system will
> waste at most 20s for such meaningless trying of freezing.
> 
> With this patch, the value of timeout can be configured to smaller
> value, so such meaningless trying of freezing will be aborted in
> earlier time, and later freezing can be also triggered in earlier
> time. And more power will be saved.
> In normal case on mobile phone, it costs real little time to freeze
> processes. On some platform, it only costs about 20ms to freeze
> user space processes and 10ms to freeze kernel freezable threads.
> 
> Signed-off-by: Liu Chuansheng <chuansheng.liu@...el.com>
> Signed-off-by: Li Fei <fei.li@...el.com>
> ---
>  Documentation/power/freezing-of-tasks.txt |    5 +++++
>  include/linux/freezer.h                   |    5 +++++
>  kernel/power/main.c                       |   27 +++++++++++++++++++++++++++
>  kernel/power/process.c                    |    4 ++--
>  4 files changed, 39 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt
> index 6ec291e..85894d8 100644
> --- a/Documentation/power/freezing-of-tasks.txt
> +++ b/Documentation/power/freezing-of-tasks.txt
> @@ -223,3 +223,8 @@ since they ask the freezer to skip freezing this task, since it is anyway
>  only after the entire suspend/hibernation sequence is complete.
>  So, to summarize, use [un]lock_system_sleep() instead of directly using
>  mutex_[un]lock(&pm_mutex). That would prevent freezing failures.
> +
> +V. Miscellaneous
> +/sys/power/pm_freeze_timeout controls how long it will cost at most to freeze
> +all user space processes or all freezable kernel threads, in unit of millisecond.
> +The default value is 20000, with range of unsigned integer.
> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
> index e4238ce..e70df40 100644
> --- a/include/linux/freezer.h
> +++ b/include/linux/freezer.h
> @@ -13,6 +13,11 @@ extern bool pm_freezing;		/* PM freezing in effect */
>  extern bool pm_nosig_freezing;		/* PM nosig freezing in effect */
>  
>  /*
> + * Timeout for stopping processes
> + */
> +extern unsigned int freeze_timeout_msecs;
> +
> +/*
>   * Check if a process has been frozen
>   */
>  static inline bool frozen(struct task_struct *p)
> diff --git a/kernel/power/main.c b/kernel/power/main.c
> index 1c16f91..3e1c9da 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -553,6 +553,30 @@ power_attr(pm_trace_dev_match);
>  
>  #endif /* CONFIG_PM_TRACE */
>  
> +#ifdef CONFIG_FREEZER
> +static ssize_t pm_freeze_timeout_show(struct kobject *kobj,
> +				      struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%u\n", freeze_timeout_msecs);
> +}
> +
> +static ssize_t pm_freeze_timeout_store(struct kobject *kobj,
> +				       struct kobj_attribute *attr,
> +				       const char *buf, size_t n)
> +{
> +	unsigned long val;
> +
> +	if (kstrtoul(buf, 10, &val))
> +		return -EINVAL;
> +
> +	freeze_timeout_msecs = val;
> +	return n;
> +}
> +
> +power_attr(pm_freeze_timeout);
> +
> +#endif	/* CONFIG_FREEZER*/
> +
>  static struct attribute * g[] = {
>  	&state_attr.attr,
>  #ifdef CONFIG_PM_TRACE
> @@ -576,6 +600,9 @@ static struct attribute * g[] = {
>  	&pm_print_times_attr.attr,
>  #endif
>  #endif
> +#ifdef CONFIG_FREEZER
> +	&pm_freeze_timeout_attr.attr,
> +#endif
>  	NULL,
>  };
>  
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index d5a258b..98088e0 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -21,7 +21,7 @@
>  /* 
>   * Timeout for stopping processes
>   */
> -#define TIMEOUT	(20 * HZ)
> +unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;
>  
>  static int try_to_freeze_tasks(bool user_only)
>  {
> @@ -36,7 +36,7 @@ static int try_to_freeze_tasks(bool user_only)
>  
>  	do_gettimeofday(&start);
>  
> -	end_time = jiffies + TIMEOUT;
> +	end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);
>  
>  	if (!user_only)
>  		freeze_workqueues_begin();
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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