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

[Dietmar Eggemann]

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
> > >      âââ pd0
> > >      â âââ cost
> > >      â âââ cpus
> > >      â âââ frequency
> > >      â âââ 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@h960:~# ls /sys/devices/system/cpu/energy_model/pd0/
cost
cpus
frequency
power

root@h960:~# 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.