From: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> > 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 <lorenzo.pieralisi@xxxxxxx> >> Date: Tue, 18 Feb 2014 11:47:31 +0000 >> > + - min-residency >> > + Usage: Required >> > + Value type: <prop-encoded-array> >> > + 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 The point is that if you compare breakeven between state 0 and state 2 the breakeven time will be smaller that when you compare the breakeven between state 1 and state 2. Assuming states ordered by "deepness" in the sense that deeper states have lower in-state power and longer entry/exit times. I guess you could specify that the min-residency defines the time when the state breaks even compared to the previous (shallower) state. --Antti -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
