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Some SoCs, such as the sd855 or the old TC2 have OPPs within the same performance domain, whose cost is higher than others with a higher frequency. If those OPPs are interesting from a cooling perspective, it makes no sense to use them when the device can run at full capacity. Those OPPs handicap the performance domain, when choosing the most energy-efficient task placement, and are wasting energy. They are inefficient. Hence, add support for such OPPs to the Energy Model, which creates for each OPP a performance state. The Energy Model can now be read using the regular table, which contains all performance states available, or using an efficient table, where inefficient performance states (and by extension, inefficient OPPs) have been removed. Currently, the efficient table is used in two paths. Schedutil, that'll skip inefficient OPPs for the frequency selection and em_cpu_energy(), used by find_energy_efficient_cpu() to estimate the energy cost for a specified task placement. We have to modify both paths in the same patch so they stay synchronized. The thermal framework still relies on the original table and hence, non CPU devices won't create the efficient table. As used in the hot-path, the efficient table is a lookup table, generated dynamically when the perf domain is created. The complexity of searching a performance state is hence changed from O(n) to O(1). This also speeds-up em_cpu_energy() even if no inefficient OPPs have been found. Signed-off-by:Vincent Donnefort <vincent.donnefort@arm.com>
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