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

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Date:   Thu, 23 Jun 2022 23:02:37 -0700
From:   Wei Wang <wvw@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-pm@...r.kernel.org
Subject: Re: [PATCH 3/3] thermal/sysfs: Remove cooling device sysfs statistics

On Fri, Jun 3, 2022 at 4:04 AM Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>
>
> 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
>
>

Sorry for the late reply, trying to catch up on emails after sick
recovery. We use it for stats collection to understand thermal
residency, and it is not in the HAL code, we don't use the transition
table heavily though. Are some of the devices having too many cooling
devices? Can we have a config to enable stats for a given cooling
device?

Thanks!
-Wei

>
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