Messages in this thread | | | From | Vincent Guittot <> | Date | Tue, 14 Apr 2020 17:43:33 +0200 | Subject | Re: [PATCH 1/4] sched/topology: Store root domain CPU capacity sum |
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On Tue, 14 Apr 2020 at 17:27, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 14.04.20 14:45, Quentin Perret wrote: > > On Wednesday 08 Apr 2020 at 19:03:57 (+0200), Vincent Guittot wrote: > >> Or we can do the opposite and only use capacity_orig_of()/rq->cpu_capacity_orig. > >> > >> Is there a case where the max cpu capacity changes over time ? So I > >> would prefer to use cpu_capacity_orig which is a field of scheduler > >> instead of always calling an external arch specific function > > > > Note however that using arch_scale_cpu_capacity() would be more > > efficient, especially on non-arm/arm64 systems where it is a > > compile-time constant. > > or essentially all ARCHs not defining it. > > > > > It's probably a matter of personal taste, but I find rq->cpu_capacity_orig > > superfluous. It wastes space without actually giving you anything no? > > Anybody remembers why it was introduced in the first place? > > v3.18 arm providing arch_scale_cpu_capacity() > v4.1 introduction of rq->cpu_capacity_orig > v4.10 arm64 providing arch_scale_cpu_capacity() > ... > > So it's down to the question of 'minimizing the scheduler calls to an > external arch function' vs 'efficiency'.
Using cpu_capacity_orig will provide more consistency because it will be set while setting the sched_domain topology
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