Re: [PATCH v1] PM / Domains: Add tracepoints

[Matthias Kaehlcke]

On Tue, Oct 01, 2019 at 01:03:43PM -0400, Steven Rostedt wrote:
> On Tue, 1 Oct 2019 09:35:42 -0700
> Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote:
> 
> > How about this instead:
> > 
> >   Add tracepoints for genpd_power_on, genpd_power_off and
> >   genpd_set_performance_state. The tracepoints can help with
> >   understanding power domain behavior of a given device, which
> >   may be particularly interesting for battery powered devices
> >   and suspend/resume.
> 
> Do you have a use case example to present?

TBH I'm not looking into a specific use case right now. While
peeking around in /sys/kernel/debug/tracing/events to learn more
about existing tracepoints that might be relevant for my work
I noticed the absence of genpd ones and it seemed a good idea to
add them preemptively. Conceptually they seem similar to the
existing regulator_enable/disable and cpu_idle tracepoints.

As an abstract use case I could see power analysis on battery
powered devices during suspend. genpd_power_on/off allow to see
which power domains remain on during suspend, and might give
insights for possible power saving options. Examples could be that
a power domain stays unexpectedly on due to a misconfiguration, or
two power domains remain on when it could be only one if you just
moved that one pin/port over to the other domain in the next
hardware revision.