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

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Date:	Thu, 13 Aug 2015 20:10:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	mingo@...hat.com, vincent.guittot@...aro.org,
	daniel.lezcano@...aro.org,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	yuyang.du@...el.com, mturquette@...libre.com, rjw@...ysocki.net,
	Juri Lelli <Juri.Lelli@....com>, sgurrappadi@...dia.com,
	pang.xunlei@....com.cn, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [RFCv5 PATCH 28/46] sched: Count number of shallower idle-states
 in struct sched_group_energy

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.

OK..

> 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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