From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lorenzo Pieralisi Subject: Re: [PATCH RFC v4 3/3] Documentation: arm: define DT idle states bindings Date: Mon, 17 Mar 2014 11:53:03 +0000 Message-ID: <20140317115303.GB28453@e102568-lin.cambridge.arm.com> References: <1392724051-11950-1-git-send-email-lorenzo.pieralisi@arm.com> <1392724051-11950-4-git-send-email-lorenzo.pieralisi@arm.com> <20140317.131507.1338341364843764791.apm@brigitte.kvy.fi> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140317.131507.1338341364843764791.apm@brigitte.kvy.fi> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Antti P Miettinen Cc: Mark Rutland , "mturquette@linaro.org" , "t.figa@samsung.com" , "mark.hambleton@broadcom.com" , "linux@arm.linux.org.uk" , "nico@linaro.org" , "daniel.lezcano@linaro.org" , "sebastian.capella@linaro.org" , "grant.likely@linaro.org" , Dave P Martin , Charles Garcia-Tobin , "devicetree@vger.kernel.org" , "khilman@linaro.org" , "linux-pm@vger.kernel.org" , "galak@codeaurora.org" , "robh+dt@kernel.org" , "vincent.guittot@linaro.org" , linux-arm-kernel@lists.infradea List-Id: linux-pm@vger.kernel.org Hi Antti, On Mon, Mar 17, 2014 at 11:15:07AM +0000, Antti P Miettinen wrote: > Sorry for having been lazy in commenting.. No worries, comments always welcome. > From: Lorenzo Pieralisi > Date: Tue, 18 Feb 2014 11:47:31 +0000 > > + - min-residency > > + Usage: Required > > + Value type: > > + Definition: u32 value representing time in microseconds > > + required for the CPU to be in the idle state to > > + break even in power consumption terms compared > > + to idle state idle_standby ([4][5]). > > To me this continues to be a bit illdefined. Say we have three states: > 0,1,2. State 0 is the idle_standby. Providing a minimum residency for > state 1 compared to state 0 sort of makes sense, but if we provide a > minimum residency for state 2 compared to state 0 the break even time > is going to be smaller than break even when comparing state 1 and > state 2. With this data we'd enter state 2 when we'd be better off > entering state 1. I am not sure I got your reply right, but min-residency for state 2 will be higher than state 1, since it has to cater for the dynamic power consumed by entering the state (but burns less power than state 1 when _in_ the state). Entering a state has a power cost and min-residency should take that into account, worst-case as per other stats. min-residency (and so the break-even) should take into account that entering the state is not for free. I think that comparing against idle_standby is the only sane way we can define that parameter, either that or we remove it. Does it make sense ? Thanks ! Lorenzo