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Date: Tue, 02 Apr 2013 13:18:27 +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 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 ? Thanks -- Daniel -- <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/
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