Messages in this thread | | | Date | Thu, 16 Aug 2018 18:27:02 +0100 | From | Patrick Bellasi <> | Subject | Re: [PATCH v3 07/14] sched/core: uclamp: enforce last task UCLAMP_MAX |
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On 16-Aug 19:10, Dietmar Eggemann wrote: > On 08/16/2018 06:47 PM, Patrick Bellasi wrote: > >On 16-Aug 17:43, Dietmar Eggemann wrote: > >>On 08/06/2018 06:39 PM, Patrick Bellasi wrote: > >>>When a util_max clamped task sleeps, its clamp constraints are removed > >>>from the CPU. However, the blocked utilization on that CPU can still be > >>>higher than the max clamp value enforced while that task was running. > >>>This max clamp removal when a CPU is going to be idle could thus allow > >>>unwanted CPU frequency increases, right while the task is not running. > >> > >>So 'rq->uclamp.flags == UCLAMP_FLAG_IDLE' means CPU is IDLE because > >>non-clamped tasks are tracked as well ((group_id = 0)). > > > >Right, but... with (group_id = 0) you mean that "non-clamped tasks are > >tracked" in the first clamp group? > > Yes. I was asking myself what will happen if there are only non-clamped > tasks runnable ...
Non clamped tasks is kind-of ambiguous, since you can have: a) tasks with util_max = UCLAMP_NOT_VALID (the default for all tasks) b) tasks with util_max = SCHED_CAPACITY_SCALE as a task specific clamp value
They are both technically not clamped but, for case b there should not be issue, since we will track SCHED_CAPACITY_SCALE as idle hold value.
For case a instead is a bit different, especially when they mix with tasks with a valid task specific clamp value, as I've just commented in this posting:
Message-ID: <20180816172016.GG2960@e110439-lin>
> > > > >>Maybe this is worth mentioning here? > > > >Maybe I can explicitely say that we detect that there are not RUNNABLE > >tasks because all the clamp groups are in UCLAMP_NOT_VALID status. > > Yes, would have helped me the grasp this earlier ...
Right, I'm going to add a bit of text on that.
Cheers Patrick
-- #include <best/regards.h>
Patrick Bellasi
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