linux-kernel - Re: [PATCH 3/3] thermal/sysfs: Remove cooling device sysfs statistics

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Message-ID: <cb35e356-bc90-2a67-6983-1a4c3a0ea62d@linaro.org>
Date:   Thu, 2 Jun 2022 10:37:47 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rafael@...nel.org, quic_manafm@...cinc.com,
        Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>, Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH 3/3] thermal/sysfs: Remove cooling device sysfs statistics


Hi Lukasz,

[Adding Todd]

On 01/06/2022 17:33, Lukasz Luba wrote:
> Hi Daniel,
> 
> 
> On 6/1/22 16:14, Daniel Lezcano wrote:
>> The statistics are for debugging purpose and belong to debugfs rather
>> than sysfs. As the previous changes introduced the same statistics in
>> debugfs, those in sysfs are no longer needed and can be removed.
> 
> I just want to let you know that in current Android kernels we cannot
> even compile the kernel with CONFIG_DEBUG_FS.

Right, it makes sense. Precisely, with the sysfs stats they are always 
compiled in for the Android kernel and is a problem for low memory 
systems. While debugfs can fulfill its purpose in the developement and 
will be removed in production systems.

> I have this pain with
> Energy Model there... Some vendors might see useful info via this
> sysfs interface in bring-up of the SoC.

Well alternatively, information can be extracted from procfs in the 
device-tree description.

What prevents to add energy information in sysfs now that the energy 
model is per device ?

> I don't know if there are user-space tools tracking this
> information via sysfs. We probably should check that.
> 
> I agree that these statistics look more like debug info, rather than
> something useful for control.
> 
> Furthermore, we have trace events for the cooling state changes, which
> should be good enough for bring-up and experiments.
> 
> I don't have strong preferences here. I tend to agree to remove this
> interface if there are no user-space tools using it.

I agree userspace can also get information about the transition but the 
goal of the debugfs is also add information about thermal internals like 
average temperature at mitigation time, min and max, timings, etc ...


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