linux-kernel - Re: [PATCH v6 04/14] PM / EM: Expose the Energy Model in sysfs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <fe196eda-5e97-b115-0c24-b484428d2ac2@arm.com>
Date:   Thu, 6 Sep 2018 17:14:57 -0700
From:   Dietmar Eggemann <dietmar.eggemann@....com>
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,
        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 v6 04/14] PM / EM: Expose the Energy Model in sysfs

On 09/06/2018 07:09 AM, Quentin Perret wrote:
> Hi Dietmar,
> 
> On Wednesday 05 Sep 2018 at 23:56:43 (-0700), Dietmar Eggemann wrote:
>> On 08/20/2018 02:44 AM, Quentin Perret 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
>>
>> cpus (cpumask of the perf domain), frequency (OPP's of the perf domain) and
>> power (values at those OPP's) are somehow easy to grasp, cost is definitely
>> not.
>>
>> You have this nice description in em_pd_energy() what cost actually is.
>> IMHO, might be worth repeating this at least in the patch header here.
> 
> Hmm, this patch introduces the sysfs interface, not the 'cost' field
> itself. As long as 'cost' is documented in the patch that introduces it
> we should be good no ? I mean this patch header tells you _where_ the
> fields of the structure are exposed. _What_ the structure is all about
> is a different story.

Mmmh, so maybe a EAS related documentation file explaining this 
interface as well, which can be introduced later is the solution here?

I'm just not 100% convinced that those cost values are self-explanatory 
like the other three items:

root@...0:~# ls /sys/devices/system/cpu/energy_model/pd0/
cost
cpus
frequency
power

root@...0:~# cat /sys/devices/system/cpu/energy_model/pd0/*
96 129 163 201 245
0-3
533000 999000 1402000 1709000 1844000
28 70 124 187 245

> But yeah, in any case, a reminder shouldn't hurt I guess, if you really
> want one :-)

Nothing which should hold this patch-set back though.