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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 02 Apr 2013 12:08:44 +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 11:37 AM, jonghwa3.lee@...sung.com wrote:
> On 2013년 04월 02일 16:34, Daniel Lezcano wrote:
> 
>> 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);
>>
> 
> 
> Yes, I did.
> 
>> ?
>>
>>> 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 for your opinion.
> 
> Actually, I work on ARM architecture and I knew that the attempt of applying
> idle notifier was failed. You probably knew it, because the link you gave me
> before is that attempt. (https://lkml.org/lkml/2012/2/7/504) :)

Yeah, now I recall this thread.

> Currently, there
> is only notifying call which is for led in arch/arm/kernel/process.c and I think
> it isn't for me to use. Anyway, Do you really think it is better way to use
> notifier than my way? Because I think it is too heavy for me. On my board,
> sometimes entering idle happened hundreds times during the 100ms. I don't want
> to call notifier that much time. IMO, just moving local variable to per-cpu
> variable for showing the enter/exit time looks better although it requires code
> modification on cpudile side.  What do you think?

Sorry, but it is hard to figure out what you are trying to achieve with
a single patch.

IIUC, you want to know how long the cpu is idle including the current
state, right ? So you need to know if the cpu is idle and when it
entered the idle state, correct ?

If the cpu is idle and the information is per cpu, how will you read
this value from another cpu without introducing a locking mechanism ?

Does it mean the cpufreq governor needs cpuidle ? I am wondering if
these informations shouldn't be retrieved from the scheduler, not from
cpuidle.

-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/