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

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Message-ID: <515A8A21.6070509@linaro.org>
Date:	Tue, 02 Apr 2013 09:34:57 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	jonghwa3.lee@...sung.com
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 04/02/2013 08:17 AM, jonghwa3.lee@...sung.com wrote:
> 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.

Did you looked at:

include/linux/sched.h:extern int idle_cpu(int cpu);

?

> 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.

I suggest you look at the enter_idle / exit_idle function and make your
governor to subscribe to the IDLE_START/EXIT notifiers.

arch/x86/kernel/process.c

These are defined for the x86 architecture, maybe worth to add it to
another architecture.

Thanks
  -- Daniel

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