Messages in this thread | | | Subject | Re: [PATCH 1/4] sched/topology: Store root domain CPU capacity sum | From | Dietmar Eggemann <> | Date | Tue, 14 Apr 2020 11:20:05 +0200 |
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On 09.04.20 16:13, Vincent Guittot wrote: > On Thu, 9 Apr 2020 at 15:50, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: >> >> On 08.04.20 19:03, Vincent Guittot wrote: >>> On Wed, 8 Apr 2020 at 18:31, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: >>>> >>>> On 08.04.20 14:29, Vincent Guittot wrote: >>>>> On Wed, 8 Apr 2020 at 11:50, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
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>> And it looks like that asym_cpu_capacity_level() [topology.c] would fail >> if we would use capacity_orig_of() instead of arch_scale_cpu_capacity(). > > Yes I agree. See below > >> post_init_entity_util_avg() [fair.c] and sugov_get_util() >> [cpufreq_schedutil.c] would be temporarily off until >> update_cpu_capacity() has updated cpu_rq(cpu)->cpu_capacity_orig. > > I think that we could even get rid of this update in > update_cpu_capacity(). cpu_capacity_orig should be set while building > the sched_domain topology because the topology itself is built based > on this max cpu capacity with asym_cpu_capacity_level(). So changing > the capacity without rebuilding the domain could break the > sched_domain topology correctness.
True. rq->cpu_capacity_orig could be set early in build_sched_domains(), before the call to asym_cpu_capacity_level() or within this function.
> And we can't really set cpu_capacity_orig earlier during the boot > because the capacity of b.L is set late during the boot and a rebuild > of the sched_domain topology is then triggered. > >> >> compute_energy() [fair.c] is guarded by sched_energy_enabled() from >> being used at startup. >> >> scale_rt_capacity() could be changed in case we call it after the >> cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(cpu) in >> update_cpu_capacity(). > > With the removal of the update in update_cpu_capacity(), we don't have > a problem anymore, isn't it ?
True.
>> The Energy Model (and CPUfreq cooling) code would need >> capacity_orig_of() exported. arch_scale_cpu_capacity() currently is >> exported via include/linux/sched/topology.h. > > Not sure that we need to export it outside scheduler, they can still > use arch_scale_cpu_capacity()
OK, let's change this for the task scheduler only.
>> I guess Pelt and 'scale invariant Deadline bandwidth enforcement' should >> continue using arch_scale_cpu_capacity() in sync with >> arch_scale_freq_capacity(). > > Why can't they use capacity_orig_of ? > we keep using arch_scale_freq_capacity() because it's dynamic but we > don't really need to keep using arch_scale_cpu_capacity()
OK, Pelt is task scheduler so it can be changed here as well.
I'm going to create a patch following these ideas.
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