Re: [PATCH V3] suspend: enable freeze timeout configuration through sys

anish singh
2013-01-31T09:52:25Z

On Thu, Jan 31, 2013 at 2:43 PM, Li, Fei <fei.li@intel.com> wrote:
>> -----Original Message-----
>> From: Yasuaki Ishimatsu [mailto:isimatu.yasuaki@jp.fujitsu.com]
>> Sent: Thursday, January 31, 2013 3:30 PM
>> To: Li, Fei
>> Cc: rjw@sisk.pl; akpm@linux-foundation.org; linux-kernel@vger.kernel.org;
>> linux-pm@vger.kernel.org; Liu, Chuansheng
>> Subject: Re: [PATCH V3] suspend: enable freeze timeout configuration through
>> sys
>>
>> 2013/01/31 13:55, fli24 wrote:
>> >
>> > 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.
>> > 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@intel.com>
>> > Signed-off-by: Li Fei <fei.li@intel.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..5a24a33 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 sys_freeze_process_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..453ead1 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", sys_freeze_process_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;
>> > +
>> > + sys_freeze_process_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..ba45a26 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 sys_freeze_process_timeout_msecs = 20000;
>>
>> 20000 does not mean 20 seconds since we can select HZ other than 1000.
>> So (20 * HZ) is better than 20000.
>>
> [Li, Fei]
> Are you sure about this, (20*HZ) better than 20000, or you mean 20 * MSEC_PER_SEC?
Yasuaki mean HZ value will not always be 1000.The value of HZ differs for each
supported architecture. In fact, on some supported architectures,
it even differs between machine types.
When writing kernel code, never assume that HZ has any given value.
Right now you are assuming that the delay will be always 20 seconds because of
your assumption of HZ.

> In fact, the usage of such variable has been changed as below in the patch:
> end_time = jiffies + msecs_to_jiffies(sys_freeze_process_timeout_msecs)
> So I don't think it make sense to use msecs_to_jiffies(20*HZ).
>
> If needed, I think we can refine it to use 20* MSEC_PER_SEC instead of 20000.
> How about your opinion?
>
> Thanks!
> Best Regards,
> Li Fei
>
>> Thanks,
>> Yasuaki Ishimatsu
>>
>> >
>> > 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(sys_freeze_process_timeout_msecs);
>> >
>> > if (!user_only)
>> > freeze_workqueues_begin();
>> >
>>
>