linux-kernel - Re: [PATCH v10 04/15] PM / EM: Expose the Energy Model in sysfs

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Date:   Tue, 11 Dec 2018 15:18:28 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     peterz@...radead.org, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        gregkh@...uxfoundation.org, mingo@...hat.com,
        dietmar.eggemann@....com, morten.rasmussen@....com,
        chris.redpath@....com, patrick.bellasi@....com,
        valentin.schneider@....com, vincent.guittot@...aro.org,
        thara.gopinath@...aro.org, viresh.kumar@...aro.org,
        tkjos@...gle.com, joel@...lfernandes.org, smuckle@...gle.com,
        adharmap@...eaurora.org, skannan@...eaurora.org,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [PATCH v10 04/15] PM / EM: Expose the Energy Model in sysfs


* Quentin Perret <quentin.perret@....com> wrote:

> Expose the Energy Model (read-only) of all performance domains in sysfs
> for convenience. To do so, add a kobject to the CPU subsystem under the
> umbrella of which a kobject for each performance domain is attached.
> 
> The resulting hierarchy is as follows for a platform with two
> performance domains for example:
> 
>    /sys/devices/system/cpu/energy_model
>    ├── pd0
>    │   ├── cost
>    │   ├── cpus
>    │   ├── frequency
>    │   └── power
>    └── pd4
>        ├── cost
>        ├── cpus
>        ├── frequency
>        └── power
> 
> In this implementation, the kobject abstraction is only used as a
> convenient way of exposing data to sysfs. However, it could also be
> used in the future to allocate and release performance domains in a more
> dynamic way using reference counting.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Signed-off-by: Quentin Perret <quentin.perret@....com>
> ---
>  include/linux/energy_model.h |  2 +
>  kernel/power/energy_model.c  | 90 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 92 insertions(+)

Why is a read-only ABI added for 'convenience'? We really don't do that 
as ABIs are final and they come with responsibilities.

I think if this is for debug purposes it should be declared and put into 
debugfs or so.

If it's for some other purpose that purpose should be declared.

Thanks,

	Ingo