Re: [RFCv5 PATCH 28/46] sched: Count number of shallower idle-states in struct sched_group_energy

From: Peter Zijlstra
Date: Thu Aug 13 2015 - 14:10:34 EST

On Tue, Jul 07, 2015 at 07:24:11PM +0100, Morten Rasmussen wrote:
> cpuidle associates all idle-states with each cpu while the energy model
> associates them with the sched_group covering the cpus coordinating
> entry to the idle-state. To look up the idle-state power consumption in
> the energy model it is therefore necessary to translate from cpuidle
> idle-state index to energy model index. For this purpose it is helpful
> to know how many idle-states that are listed in lower level sched_groups
> (in struct sched_group_energy).
> Example: ARMv8 big.LITTLE JUNO (Cortex A57, A53) idle-states:
> Idle-state cpuidle Energy model table indices
> index per-cpu sg per-cluster sg
> WFI 0 0 (0)
> Core power-down 1 1 0*
> Cluster power-down 2 (1) 1
> For per-cpu sgs no translation is required. If cpuidle reports state
> index 0 or 1, the cpu is in WFI or core power-down, respectively. We can
> look the idle-power up directly in the sg energy model table.


> Idle-state
> cluster power-down, is represented in the per-cluster sg energy model
> table as index 1. Index 0* is reserved for cluster power consumption
> when the cpus all are in state 0 or 1, but cpuidle decided not to go for
> cluster power-down.

0* is not an integer.

> Given the index from cpuidle we can compute the
> correct index in the energy model tables for the sgs at each level if we
> know how many states are in the tables in the child sgs. The actual
> translation is implemented in a later patch.

And you've lost me... I've looked at that later patch (its the next one)
and I cannot say I'm less confused.
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