linux-kernel - Re: [PATCH v2 0/3] EM / PM: Inefficient OPPs

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Message-ID: <a5882c26-ad1c-8e95-e529-f45fcc46099f@arm.com>
Date:   Thu, 27 May 2021 08:13:09 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Vincent Donnefort <vincent.donnefort@....com>,
        peterz@...radead.org, rjw@...ysocki.net,
        vincent.guittot@...aro.org, qperret@...gle.com,
        linux-kernel@...r.kernel.org, ionela.voinescu@....com,
        dietmar.eggemann@....com
Subject: Re: [PATCH v2 0/3] EM / PM: Inefficient OPPs

Hi Viresh,

On 5/26/21 10:33 AM, Viresh Kumar wrote:
> On 26-05-21, 09:56, Lukasz Luba wrote:
>> No, these OPPs have to stay because they are used in thermal for cooling
>> states.
> 
> This won't break the thermal tables. Thermal just sets the max-freq for a CPU,
> and it doesn't depend on the OPP table for that.
> 
>> DT cooling devices might have them set as a scope of possible
>> states. We don't want to break existing platforms, don't we?
> 
> I don't think we will end up breaking anything here.
> 
>> We want to 'avoid' those OPPs when possible (no thermal pressure), but
>> we might have to use them sometimes.
> 
> Why would we want to use them if they are inefficient ? Thermal or something
> else as well ?
> 
> More in the other reply I am sending to Vincent.
> 

I have responded to your email there. I don't know if you have seen it.
As I said there, these OPPs, which from energy perspective we call
'inefficient', might be used to provide enough performance under thermal
constraints.

Regards,
Lukasz