linux-kernel - Re: [PATCH 2/2] cpufreq: Update CPU capacity reduction in store_scaling_max

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Date:   Tue, 11 Oct 2022 10:38:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-kernel@...r.kernel.org, rafael@...nel.org,
        linux-pm@...r.kernel.org, Dietmar.Eggemann@....com,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 2/2] cpufreq: Update CPU capacity reduction in
 store_scaling_max_freq()

On Mon, Oct 10, 2022 at 11:46:29AM +0100, Lukasz Luba wrote:
> 
> +CC Daniel, since I have mentioned a few times DTPM
> 
> On 10/10/22 11:25, Peter Zijlstra wrote:
> > On Mon, Oct 10, 2022 at 11:12:06AM +0100, Lukasz Luba wrote:
> > > BTW, those Android user space max freq requests are not that long,
> > > mostly due to camera capturing (you can see a few in this file,
> > > e.g. [1]).
> > 
> > It does what now ?!? Why is Android using this *at*all* ?
> 
> It tries to balance the power budget, before bad things happen
> randomly (throttling different devices w/o a good context what's
> going on). Please keep in mind that we have ~3 Watts total power
> budget in a phone, while several devices might be suddenly used:
> 1. big CPU with max power ~3-3.5 Watts (and we have 2 cores on pixel6)
> 2. GPU with max power ~6Watts (normally ~1-2Watts when lightly used)
> 3. ISP (Image Signal Processor) up to ~2Watts
> 4. DSP also up to 1-2Watts
> 
> We don't have currently a good mechanism which could be aware
> of the total power/thermal budget and relations between those
> devices. Vendors and OEMs run experiments on devices and profile
> them to work more predictable in those 'important to users' scenarios.
> 
> AFAIK Daniel Lescano is trying to help with this new interface
> for PowerCap: DTMP. It might be use as a new interface for those known
> scenarios like the camera snapshot. But that interface is on the list
> that I have also mentioned - it's missing the notification mechanism
> for the scheduler reduced capacity due to user-space new scenario.

DTMP is like IPA but including random devices? Because I thought IPA
already did lots of this.