From mboxrd@z Thu Jan 1 00:00:00 1970 From: asinghal@codeaurora.org Subject: Re: [RFC] Unprepare callback for cpuidle_device Date: Mon, 11 Jul 2011 10:26:56 -0700 (PDT) Message-ID: <473338c2d56302337f83871ce1c201e4.squirrel@www.codeaurora.org> References: <4E15516E.5040209@gmail.com> <82b596dce7b84db206d3afb6da564fb9.squirrel@www.codeaurora.org> <4E170010.2000403@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4E170010.2000403@linux.vnet.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: Deepthi Dharwar Cc: linux-pm@lists.linux-foundation.org, asinghal@codeaurora.org, johlstei@codeaurora.org List-Id: linux-pm@vger.kernel.org hello Deepthi, please see my replies inline: > Hi Amar, > > On Friday 08 July 2011 01:22 AM, asinghal@codeaurora.org wrote: >> Hello Trinabh, >> i cannot use the enter callback due to the following >> reason: >> >> the residency calculation(tick)nohz_get_sleep_length) and the idle state >> selection happens in the menu governor. The enter callback is called >> with >> the selected state. > > One would first execute prepare then call select and enter . > So in the newer proposed code, there is no prepare routine. One would > just execute select() and then enter() (Prepare functionality is part of > the > enter routine itself) Is it not possible to cancel the timer, > calculate the execute nohz_get_sleep in enter routine again, > then select the idle state depending on the time . Automatically promote > or demote > idle state based on the latest value returned in the driver ? > Cancelling the timer and calculating the sleep length again in the enter callback is possible; but what does not make sense is calling the select routine again ; definitely the select routine of the governor needs to be called only once. And actually, the sleep length is calculated in the function tick_nohz_stop_sched_tick.( so shld the prepare callback be moved before that in cpu_idle ??) I am looking for a nice way to cancel and restart the high resolution timers in the idle code; even if that means rearranging the cpu_idle code. Another way i was looking to solve this issue was add deferrable feature to HR timers; if someone has thoughts on that please chime in. thanks, amar >> So cancelling the hrtimer that would affect the residency value >> calculated >> in the menu governor, in the enter callback is not possible. The timer >> needs to be cancelled before the select call is made. >> >> thanks, >> amar >> >> >> >>> On 07/06/2011 04:23 PM, asinghal@codeaurora.org wrote: >>>> We plan to use high resolution timers in one of our modules, with the >>>> requirement that we cancel these timers when the cpu goes idle and >>>> restart >>>> them when the cpu comes out of idle. >>>> >>>> We are cancelling the timers in cpuidle prepare callback. The problem >>>> is >>>> that if the need_resched() call in drivers/cpuidle/cpuidle.c returns >>>> true, >>>> how do we restart the timer? If the call returns false, we can restart >>>> the >>>> timer in the cpuidle enter callback. >>> >>> Hi Amar, >>> >>> I think you should not use cpuidle prepare callback at all. It may be >>> removed soon (see https://lkml.org/lkml/2011/6/6/261) and I think >>> there are better ways to achieve what you are trying to do. >>> >>> I think everything should go into the enter routines (the idle routines >>> provided by the driver). That way you would not have to worry about >>> need_resched() in cpuidle.c. Also it would be a cleaner implementation >>> as you wouldn't touch generic cpuidle code. >>> >>>> >>>> The solution to the problem that we have in mind is adding an >>>> unprepare >>>> callback to the cpuidle_device struct, and calling it if >>>> needs_resched() >>>> returns true. Another option is to implement deferred timers for >>>> hrtimers. >>>> Which of the two options is the better solution, or is there another >>>> feasible alternative? >>> >>> As i said, everything should go inside enter routine and >>> you wouldn't have to use/implement prepare/unprepare callbacks. >>> >>> Thanks >>> -Trinabh >>> >> >> >> _______________________________________________ >> linux-pm mailing list >> linux-pm@lists.linux-foundation.org >> https://lists.linux-foundation.org/mailman/listinfo/linux-pm > Regards, > Deepthi >