linux-kernel - Re: [PATCH v2 04/11] sched: Allow all archs to set the power

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Date:	Thu, 05 Jun 2014 09:59:21 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
CC:	"peterz@...radead.org" <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"efault@....de" <efault@....de>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2 04/11] sched: Allow all archs to set the power_orig

[...]
>> Firstly, we need to scale cpu power in update_cpu_power() regarding
>> uArch, frequency and rt/irq pressure.
>> Here the freq related value we get back from arch_scale_freq_power(...,
>> cpu) could be an instantaneous value (curr_freq(cpu)/max_freq(cpu)).
>>
>> Secondly, to be able to scale the runnable avg sum of a sched entity
>> (se->avg->runnable_avg_sum), we preferable have a coefficient
>> representing uArch diffs (cpu_power_orig(cpu)/cpu_power_orig(most
>> powerful cpu in the system) and another coefficient (avg freq over 'now
> 
> AFAICT, the coefficient representing uArch diffs is already taken into
> account into power_freq thanks to scale_cpu, isn't it ?

True, but I can't see how the current signature of
arch_scale_cpu_power() and arch_scale_freq_power() fit into this uArch
and freq invariant updating of se->avg->runnable_avg_sum business.

>> - sa->last_runnable_update'(cpu)/max_freq(cpu). This value would have to
>> be retrieved from the arch in __update_entity_runnable_avg().
>>
[...]

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