linux-kernel - Re: [RFC PATCH 1/2] cpuidle: Add idle enter/exit time stamp for notifying current idle state.

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Date:	Tue, 02 Apr 2013 15:17:32 +0900
From:	jonghwa3.lee@...sung.com
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, cpufreq@...r.kernel.org,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Lukasz Majewski <l.majewski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>, sw0312.kim@...sung.com,
	m.szyprowski@...sung.com
Subject: Re: [RFC PATCH 1/2] cpuidle: Add idle enter/exit time stamp for
 notifying current idle state.

On 2013년 04월 02일 14:00, Daniel Lezcano wrote:

> On 04/01/2013 10:24 AM, Jonghwa Lee wrote:
>> This patch adds idle state time stamp to cpuidle device structure to
>> notify its current idle state. If last enter time is newer than last
>> exit time, then it means that the core is in idle now.
>>
>> Signed-off-by: Jonghwa Lee <jonghwa3.lee@...sung.com>
>> ---
> 
> The patch description does not explain what problem you want to solve,
> how to solve it and the patch itself shows nothing.
> 
> Could you elaborate ?


I'm sorry for lacking description. I supplement more.

This patch does add time-stamp for idle enter/exit only nothing more.
The reason why I needed them is that I wanted to know current cpu idle
state. It is hard to know whether cpu is in idle or not now.
When I check the cpuidle state usage, sometimes the information is wrong.
Because it is updated only when the cpu exits the idle state. So while the
cpu is idling, the cpuidle state usage holds past one. Therefore I put
the time-stamp for cpuidle enter/exit for checking current idling and
calculating idle state usage correctly.

I just make this patch temporary for my cpufreq governor work. So, it just
use time-stamp for all idle state together. After RFC working, I have a plan
to update this patch to use timestamp for each idle state.

Thanks,


And it also can be used to calculate cpuidle state usage even the cpu is idling.
I knew the code looks worthless, but as this patchset is just
suggesting idea,


> 
> Thanks
>   -- Daniel
> 
>>  drivers/cpuidle/cpuidle.c |    8 ++++----
>>  include/linux/cpuidle.h   |    4 ++++
>>  2 files changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index eba6929..1e830cc 100644
>> --- a/drivers/cpuidle/cpuidle.c
>> +++ b/drivers/cpuidle/cpuidle.c
>> @@ -233,18 +233,18 @@ int cpuidle_wrap_enter(struct cpuidle_device *dev,
>>  				int (*enter)(struct cpuidle_device *dev,
>>  					struct cpuidle_driver *drv, int index))
>>  {
>> -	ktime_t time_start, time_end;
>>  	s64 diff;
>>  
>> -	time_start = ktime_get();
>> +	dev->last_idle_start = ktime_get();
>>  
>>  	index = enter(dev, drv, index);
>>  
>> -	time_end = ktime_get();
>> +	dev->last_idle_end = ktime_get();
>>  
>>  	local_irq_enable();
>>  
>> -	diff = ktime_to_us(ktime_sub(time_end, time_start));
>> +	diff = ktime_to_us(ktime_sub(dev->last_idle_end,
>> +				dev->last_idle_start));
>>  	if (diff > INT_MAX)
>>  		diff = INT_MAX;
>>  
>> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
>> index 480c14d..d1af05f 100644
>> --- a/include/linux/cpuidle.h
>> +++ b/include/linux/cpuidle.h
>> @@ -16,6 +16,7 @@
>>  #include <linux/kobject.h>
>>  #include <linux/completion.h>
>>  #include <linux/hrtimer.h>
>> +#include <linux/ktime.h>
>>  
>>  #define CPUIDLE_STATE_MAX	8
>>  #define CPUIDLE_NAME_LEN	16
>> @@ -74,6 +75,9 @@ struct cpuidle_device {
>>  	struct kobject		kobj;
>>  	struct completion	kobj_unregister;
>>  
>> +	ktime_t			last_idle_start;
>> +	ktime_t			last_idle_end;
>> +
>>  #ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
>>  	int			safe_state_index;
>>  	cpumask_t		coupled_cpus;
>>
> 
> 


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