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

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Date:   Fri, 3 Jun 2022 13:04:39 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Todd Kjos <tkjos@...gle.com>, 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>, Wei Wang <wvw@...gle.com>
Subject: Re: [PATCH 3/3] thermal/sysfs: Remove cooling device sysfs statistics

Hi Todd,

[adding Wei]

On 02/06/2022 21:02, Todd Kjos wrote:
> On Thu, Jun 2, 2022 at 2:16 AM Lukasz Luba <lukasz.luba@....com> wrote:

[ ... ]

>> I see, it makes sense. Let's see if Todd and Android folks don't
>> use this thermal sysfs stats, so we could remove them.
> 
> Android HALs do use the thermal sysfs stats. debugfs isn't a viable
> replacement since debugfs must not be mounted during normal operation.

Thanks for your answer.

I'm curious, what is the purpose of getting the statistics, especially 
the transitions stats from normal operation?

There were some complains about systems having a high number of cooling 
devices with a lot of states. The state transitions are represented as a 
matrix and result in up to hundred of megabytes of memory wasted.

Moreover, sysfs being limited a page size, the output is often truncated.

As it is automatically enabled for GKI, this waste of memory which is 
not negligible for system with low memory can not be avoided.

I went through the thermal HAL but did not find an usage of these 
statistics, do you have a pointer to the code using them ?

Thanks

   -- Daniel

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