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Date: Fri, 22 Jul 2022 18:49:14 +0200 From: "Rafael J. Wysocki" <rafael@...nel.org> To: "Zhang, Rui" <rui.zhang@...el.com> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>, "rafael@...nel.org" <rafael@...nel.org>, "quic_manafm@...cinc.com" <quic_manafm@...cinc.com>, "amitk@...nel.org" <amitk@...nel.org>, "lukasz.luba@....com" <lukasz.luba@....com>, "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v3 3/4] thermal/core: Build ascending ordered indexes for the trip points On Fri, Jul 22, 2022 at 9:16 AM Zhang, Rui <rui.zhang@...el.com> wrote: > > > > > -----Original Message----- > > From: Daniel Lezcano <daniel.lezcano@...aro.org> > > Sent: Thursday, July 21, 2022 5:35 PM > > To: Zhang, Rui <rui.zhang@...el.com>; rafael@...nel.org > > Cc: quic_manafm@...cinc.com; amitk@...nel.org; lukasz.luba@....com; > > linux-pm@...r.kernel.org; linux-kernel@...r.kernel.org > > Subject: Re: [PATCH v3 3/4] thermal/core: Build ascending ordered indexes > > for the trip points > > Importance: High > > > > On 19/07/2022 16:17, Zhang Rui wrote: > > > On Tue, 2022-07-19 at 09:22 +0200, Daniel Lezcano wrote: > > >> On 19/07/2022 03:14, Zhang Rui wrote: > > >>> On Mon, 2022-07-18 at 15:21 +0200, Daniel Lezcano wrote: > > >>>> > > >>>> Hi Zhang, > > >>>> > > >>>> thanks for the review > > >>>> > > >>>> On 18/07/2022 07:28, Zhang Rui wrote: > > >>>>> On Fri, 2022-07-15 at 23:09 +0200, Daniel Lezcano wrote: > > >>>> > > >>>> [ ... ] > > >>>> > > >>>>>> Instead of taking the risk of breaking the existing platforms, > > >>>>>> use an array of temperature ordered trip identifiers and make it > > >>>>>> available for the code needing to browse the trip points in an > > >>>>>> ordered way. > > >>>>>> > > >>>>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org> > > >>>>>> --- > > >>>> > > >>>> [ ... ] > > >>>> > > >>>>>> +static void sort_trips_indexes(struct thermal_zone_device > > >>>>>> *tz) > > >>>>>> +{ > > >>>>>> + int i, j; > > >>>>>> + > > >>>>>> + for (i = 0; i < tz->trips; i++) > > >>>>>> + tz->trips_indexes[i] = i; > > >>>>>> + > > >>>>>> + for (i = 0; i < tz->trips; i++) { > > >>>>>> + for (j = i + 1; j < tz->trips; j++) { > > >>>>>> + int t1, t2; > > >>>>>> + > > >>>>>> + tz->ops->get_trip_temp(tz, tz- > > >>>>>>> trips_indexes[i], &t1); > > >>>>> > > >>>>> This line can be moved to the upper loop. > > >>>> > > >>>> Right, thanks! > > >>>> > > >>>>>> + tz->ops->get_trip_temp(tz, tz- > > >>>>>>> trips_indexes[j], &t2); > > >>>>>> + > > >>>>> > > >>>>> what about the disabled trip points? > > >>>>> > > >>>>> we should ignore those trip points and check the return value to > > >>>>> make sure we're comparing the valid trip_temp values. > > >>>> > > >>>> We don't have to care about, whatever the position, the > > >>>> corresponding trip id will be disabled by the trip init function > > >>>> before calling this one and ignored in the handle_thermal_trip() > > >>>> function > > >>> > > >>> hah, I missed this one and replied to your latest reply directly. > > >>> > > >>> The thing I'm concerning is that if we don't check the return value, > > >>> for a disabled trip point, the trip_temp (t1/t2) returned is some > > >>> random value, it all depends on the previous value set by last > > >>> successful .get_trip_temp(), and this may screw up the sorting. > > >> > > >> The indexes array is the same size as the trip array, that makes the > > >> code much less prone to errors. > > >> > > >> To have the same number of trip points, the index of the disabled > > >> trip must be inserted also in the array. We don't care about its > > >> position in the indexes array because it is discarded in the > > >> handle_trip_point() function anyway. For this reason, the random > > >> temperature of the disabled trip point and the resulting position in > > >> the sorting is harmless. > > >> > > >> It is made on purpose to ignore the return value, so we have a > > >> simpler code. > > >> > > > Let's take below case for example, > > > say, we have three trip points 0, 1, 2, and trip point 1 is broken and > > > disabled. > > > > > > trip temp for trip point 0 is 10 and for trip point 2 is 20. > > > .get_trip_temp(tz, 1, &t) fails, and t is an uninitialized random > > > value > > > > > > > > > Initial: > > > trip_indexes[0]=0,trip_indexes[1]=1,trip_indexes[2]=2 > > > step1: > > > i=0,j=1 > > > get trip temp for trip point trip_indexes[0]=0 and trip_indexes[1]=1 > > > trip point 1 returns trip temp 5, and it swaps with trip point 0 > > > so > > > trip_indexes[0]=1,trip_indexes[1]=0,trip_indexes[2]=2 > > > step2: > > > i=0,j=2 > > > get trip temp for trip point trip_indexes[0]=1 and trip_indexes[2]=2 > > > trip point 1 returns trip temp 25, and it swaps with trip point 2 > > > so > > > trip_indexes[0]=2,trip_indexes[1]=0,trip_indexes[2]=1 > > > > > > And the sorting is broken now. > > > > > > please correct me if I'm missing anything. > > > > Oh, nice! Thanks for the detailed explanation. > > > > We can initialize t1 and t2 to INT_MAX, so if the get_trip_temp() fails, they > > will be set to the maximum temperature and it will be at the end of the array. > > > > Alternatively, we check the disabled bit and set the temperature to INT_MAX. > > IMO, we can > 1. get the trip temp for each trip point and cache them > 2. set the trips_disabled bit > 3. do the sorting using the cached trip temp values > in thermal_zone_device_trip_init() altogether. What about the case when the trip temperature can be set from user space? I guess we replace the cached value then, but it may be necessary to sort them again in theory?
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