linux-kernel - Re: [PATCH v3 3/3] [RFC] CPUFreq: Add support for cpu-perf-dependencies

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Date:   Mon, 16 Nov 2020 11:33:13 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Nicola Mazzucato <nicola.mazzucato@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        sudeep.holla@....com, rjw@...ysocki.net, vireshk@...nel.org,
        robh+dt@...nel.org, sboyd@...nel.org, nm@...com,
        daniel.lezcano@...aro.org, morten.rasmussen@....com,
        chris.redpath@....com
Subject: Re: [PATCH v3 3/3] [RFC] CPUFreq: Add support for
 cpu-perf-dependencies



On 11/9/20 6:57 AM, Viresh Kumar wrote:
> On 06-11-20, 11:14, Lukasz Luba wrote:
>> I also had similar doubts, because if we make frequency requests
>> independently for each CPU, why not having N cooling devs, which
>> will set independently QoS max freq for them...
>>
>> What convinced me:
>> EAS and FIE would know the 'real' frequency of the cluster, IPA
>> can use it also and have only one cooling device per cluster.
>>
>> We would like to keep this old style 'one cooling device per cpuset'.
>> I don't have strong opinion and if it would appear that there are
>> some errors in freq estimation for cluster, then maybe it does make
>> more sense to have cdev per CPU...
> 
> Let me rephrase my question. What is it that doesn't work _correctly_
> with cdev per cpufreq policy in your case? What doesn't work well if
> the thermal stuff keeps looking at only the related_cpus thing and not
> the cpu-perf-dependencies thing?
> 

We don't have a platform which would be this per-cpu freq request, yet.
Thus it's hard to answer your question. The EAS would work in 'old
style' - cluster mode. I don't know how IPA would work on such HW
and SW configuration. To figure this out I need a real platform.