From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [RFC PATCH 1/2] cpuidle: Add idle enter/exit time stamp for notifying current idle state. Date: Tue, 02 Apr 2013 12:08:44 +0200 Message-ID: <515AAE2C.3040407@linaro.org> References: <1364804657-16590-1-git-send-email-jonghwa3.lee@samsung.com> <1364804657-16590-2-git-send-email-jonghwa3.lee@samsung.com> <515A65DB.8070803@linaro.org> <515A77FC.70008@samsung.com> <515A8A21.6070509@linaro.org> <515AA6C3.3060408@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <515AA6C3.3060408@samsung.com> Sender: linux-kernel-owner@vger.kernel.org To: jonghwa3.lee@samsung.com Cc: "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, cpufreq@vger.kernel.org, MyungJoo Ham , Lukasz Majewski , Kyungmin Park , Chanwoo Choi , sw0312.kim@samsung.com, m.szyprowski@samsung.com List-Id: linux-pm@vger.kernel.org On 04/02/2013 11:37 AM, jonghwa3.lee@samsung.com wrote: > On 2013=EB=85=84 04=EC=9B=94 02=EC=9D=BC 16:34, Daniel Lezcano wrote: >=20 >> On 04/02/2013 08:17 AM, jonghwa3.lee@samsung.com wrote: >>> On 2013=EB=85=84 04=EC=9B=94 02=EC=9D=BC 14:00, Daniel Lezcano wrot= e: >>> >>>> 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 l= ast >>>>> exit time, then it means that the core is in idle now. >>>>> >>>>> Signed-off-by: Jonghwa Lee >>>>> --- >>>> >>>> The patch description does not explain what problem you want to so= lve, >>>> 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 mor= e. >>> The reason why I needed them is that I wanted to know current cpu i= dle >>> 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); >> >=20 >=20 > Yes, I did. >=20 >> ? >> >>> 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 wh= ile 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 a= nd >>> 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 ha= ve 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 y= our >> 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. >> >=20 >=20 > Thanks for your opinion. >=20 > Actually, I work on ARM architecture and I knew that the attempt of a= pplying > 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 b= oard, > sometimes entering idle happened hundreds times during the 100ms. I d= on't want > to call notifier that much time. IMO, just moving local variable to p= er-cpu > variable for showing the enter/exit time looks better although it req= uires 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. --=20 Linaro.org =E2=94=82 Open source software for= ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog