[PATCH RFC 3/3] PM / Domains: Introduce generic PM domain for cpu domain
khilman at kernel.org
Wed Jun 10 10:01:10 PDT 2015
Krzysztof Kozlowski <k.kozlowski at samsung.com> writes:
> W dniu 05.06.2015 o 07:29, Lina Iyer pisze:
>> Generally cpus are grouped under a power domain in a SoC. When all cpus
>> in the domain are in their power off state,
> What do you exactly mean here by "CPU in power off state"? How does it
> map to kernel understanding of CPU device (hotplug? cpuidle?)?
>> the cpu domain can also be
>> powered off. Genpd provides the framework for defining cpus as devices
>> that are part of a cpu domain.
> The problem which is solved looks to me like the same problem which
> coupled cpuidle tried to solve: a certain deep sleep mode (e.g. power
> off) can be entered when whole cluster is idle or other CPUs in cluster
> are powered off completely.
> It seems a little like duplicating the effort around coupled cpuidle.
Yes, it duplicates some aspects of coupled idle states, but coupled
states have their own limitations:
- only handles CPUs, not other devices sharing a power rail (e.g. L2$,
GIC, floating point unit, CoreSight, etc. etc.)
- not scaling well past 2 CPUs
- doesn't handle clusters: While this series only addresses CPUs
currently, the approach can be extended. Because genpd handles nested
domains, the could be used to model clusters as well.
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