Messages in this thread | | | Subject | Re: [Patch v5 2/6] sched/fair: Add infrastructure to store and update instantaneous thermal pressure | From | Thara Gopinath <> | Date | Wed, 6 Nov 2019 12:53:15 -0500 |
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On 11/06/2019 07:50 AM, Dietmar Eggemann wrote: > On 05/11/2019 22:53, Ionela Voinescu wrote: >> On Tuesday 05 Nov 2019 at 16:29:32 (-0500), Thara Gopinath wrote: >>> On 11/05/2019 04:15 PM, Ionela Voinescu wrote: >>>> On Tuesday 05 Nov 2019 at 16:02:00 (-0500), Thara Gopinath wrote: >>>>> On 11/05/2019 03:21 PM, Ionela Voinescu wrote: >>>>>> Hi Thara, >>>>>> >>>>>> On Tuesday 05 Nov 2019 at 13:49:42 (-0500), Thara Gopinath wrote: >>>>>> [...] >>>>>>> +static void trigger_thermal_pressure_average(struct rq *rq) >>>>>>> +{ >>>>>>> +#ifdef CONFIG_SMP >>>>>>> + update_thermal_load_avg(rq_clock_task(rq), rq, >>>>>>> + per_cpu(thermal_pressure, cpu_of(rq))); >>>>>>> +#endif >>>>>>> +} >>>>>> >>>>>> Why did you decide to keep trigger_thermal_pressure_average and not >>>>>> call update_thermal_load_avg directly? >>>>>> >>>>>> For !CONFIG_SMP you already have an update_thermal_load_avg function >>>>>> that does nothing, in kernel/sched/pelt.h, so you don't need that >>>>>> ifdef. >>>>> Hi, >>>>> >>>>> Yes you are right. But later with the shift option added, I shift >>>>> rq_clock_task(rq) by the shift. I thought it is better to contain it in >>>>> a function that replicate it in three different places. I can remove the >>>>> CONFIG_SMP in the next version. >>>> >>>> You could still keep that in one place if you shift the now argument of >>>> ___update_load_sum instead. >>> >>> No. I cannot do this. The authors of the pelt framework prefers not to >>> include a shift parameter there. I had discussed this with Vincent earlier. >>> >> >> Right! I missed Vincent's last comment on this in v4. >> >> I would argue that it's more of a PELT parameter than a CFS parameter >> :), where it's currently being used. I would also argue that's more of a >> PELT parameter than a thermal parameter. It controls the PELT time >> progression for the thermal signal, but it seems more to configure the >> PELT algorithm, rather than directly characterize thermals. >> >> In any case, it only seemed to me that adding a wrapper function for >> this purpose only was not worth doing. > > Coming back to the v4 discussion > https://lore.kernel.org/r/379d23e5-79a5-9d90-0fb6-125d9be85e99@arm.com > > There is no API between pelt.c and other parts of the scheduler/kernel > so why should we keep an unnecessary parameter and wrapper functions? > > There is also no abstraction, update_thermal_load_avg() in pelt.c even > carries '_thermal_' in its name. > > So why not define this shift value '[sched_|pelt_]thermal_decay_shift' > there as well? It belongs to update_thermal_load_avg(). > > All call sites of update_thermal_load_avg() use 'rq_clock_task(rq) >> > sched_thermal_decay_shift' so I don't see the need to pass it in. > > IMHO, preparing for eventual code changes (e.g. parsing different now > values) is not a good practice in the kernel. Keeping the code small and > tidy is.
I think we are going in circles on this one. I acknowledge you have an issue. That being said, I also understand the need to keep the pelt framework code tight. Also Ionela pointed out that there could be a need for a faster decay in which case it could mean a left shift leading to further complications if defined in pelt.c (I am not saying that I will implement a faster decay in this patch set but it is more of a future extension if needed!)
I can make trigger_thermal_pressure_average inline if that will alleviate some of the concerns.
I would also urge you to reconsider the merits of arguing this point back and forth. >
-- Warm Regards Thara
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