linux-kernel - Re: [PATCH V2] ARM: cpuidle: Support asymmetric idle definition

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Date:   Fri, 2 Jun 2017 11:25:16 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>, rjw@...ysocki.net,
        lorenzo.pieralisi@....com
Cc:     leo.yan@...aro.org,
        "open list:CPUIDLE DRIVERS" <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] ARM: cpuidle: Support asymmetric idle definition

On 02/06/2017 11:20, Sudeep Holla wrote:
> 
> 
> On 01/06/17 12:39, Daniel Lezcano wrote:
>> Some hardware have clusters with different idle states. The current code does
>> not support this and fails as it expects all the idle states to be identical.
>>
>> Because of this, the Mediatek mtk8173 had to create the same idle state for a
>> big.Little system and now the Hisilicon 960 is facing the same situation.
>>
>> Solve this by simply assuming the multiple driver will be needed for all the
>> platforms using the ARM generic cpuidle driver which makes sense because of the
>> different topologies we can support with a single kernel for ARM32 or ARM64.
>>
>> Every CPU has its own driver, so every single CPU can specify in the DT the
>> idle states.
>>
>> This simple approach allows to support the future dynamIQ system, current SMP
>> and HMP.
>>
>> It is unoptimal from a memory point of view for a system with a large number of
>> CPUs but nowadays there is no such system with a cpuidle driver on ARM.
>>
> 
> While I agree this may be simple solution, but just not necessary for
> systems with symmetric idle states especially one with large number of
> CPUs. I don't like to see 96 CPU Idle driver on say ThunderX. So we
> *must* have some basic distinction done here.
> 
> IMO, we can't punish a large SMP systems just because they don't have
> asymmetric idle states.

Can you point me in the upstream kernel a DTS with 96 cpus and using the
cpuidle-arm driver ?



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