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Message-id: <515BC7C0.3090009@samsung.com> Date: Wed, 03 Apr 2013 15:10:08 +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 20:18, Daniel Lezcano wrote: > On 04/02/2013 01:07 PM, jonghwa3.lee@...sung.com wrote: >> On 2013년 04월 02일 19:08, Daniel Lezcano wrote: >> >>> 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. >>> >> >> >> Oh my, I thought you gave the link but you didn't. It was Viresh Kumar from >> other patch of the patchset. Sorry. >> >>>> 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 ? >>> >> >> >> Exactly. >> >> >>> 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 ? >>> >> >> >> I think it might be tolerated for incoherency of that data. Governor reads the >> data only, and if recoded start time or end time are different in few usec with >> real one then it doesn't effect to the result much. >> >> >>> Does it mean the cpufreq governor needs cpuidle ? I am wondering if >>> these informations shouldn't be retrieved from the scheduler, not from >>> cpuidle. >>> >> >> >> Yes, tick_sched per-cpu variable has all information that I need. But it isn't >> global variable. And I'm afraid to change static variable to global one as my >> pleases. > > It is a global variable but there is a function to get access: > > extern struct tick_sched *tick_get_tick_sched(int cpu); > > Does it fit better for what you want to achieve ? Yes, it seems exactly what I needed. I'll check it. Thanks for your advice :) Thanks, Jonghwa. > > Thanks > -- Daniel > > -- 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/
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