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

[Lukasz Luba]

On 6/2/22 09:37, Daniel Lezcano wrote:
> Hi Lukasz,
>
> [Adding Todd]
>
> On 01/06/2022 17:33, Lukasz Luba wrote:
> > Hi Daniel,
> >
> >
> > On 6/1/22 16:14, Daniel Lezcano wrote:
> > > The statistics are for debugging purpose and belong to debugfs rather
> > > than sysfs. As the previous changes introduced the same statistics in
> > > debugfs, those in sysfs are no longer needed and can be removed.
> >
> > I just want to let you know that in current Android kernels we cannot
> > even compile the kernel with CONFIG_DEBUG_FS.
>
> Right, it makes sense. Precisely, with the sysfs stats they are always 
> compiled in for the Android kernel and is a problem for low memory 
> systems. While debugfs can fulfill its purpose in the developement and 
> will be removed in production systems.

True.

> > I have this pain with
> > Energy Model there... Some vendors might see useful info via this
> > sysfs interface in bring-up of the SoC.
>
> Well alternatively, information can be extracted from procfs in the 
> device-tree description.
>
> What prevents to add energy information in sysfs now that the energy 
> model is per device ?

Probably nothing, but we need strong need. I have proposed this
a few times internally, but this must have a requirement.
If a user-space tool would ask for it, then I could send a patch
exposing the sysfs. So far we have only one user-space tool, which
suffers the missing debugfs EM dir: LISA (but we are working on a
workaround for it).
If you have a tool or plan to have such, which uses EM, please let
me know. I'm gathering the requirements.

> > I don't know if there are user-space tools tracking this
> > information via sysfs. We probably should check that.
> >
> > I agree that these statistics look more like debug info, rather than
> > something useful for control.
> >
> > Furthermore, we have trace events for the cooling state changes, which
> > should be good enough for bring-up and experiments.
> >
> > I don't have strong preferences here. I tend to agree to remove this
> > interface if there are no user-space tools using it.
>
> I agree userspace can also get information about the transition but the 
> goal of the debugfs is also add information about thermal internals like 
> average temperature at mitigation time, min and max, timings, etc ...

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.