linux-kernel - Re: [PATCH v1] PM / Domains: Add tracepoints

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Message-ID: <20191001193701.GD87296@google.com>
Date:   Tue, 1 Oct 2019 12:37:01 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Douglas Anderson <dianders@...omium.org>,
        linux-pm@...r.kernel.org, Amit Kucheria <amit.kucheria@...aro.org>,
        linux-kernel@...r.kernel.org,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>
Subject: Re: [PATCH v1] PM / Domains: Add tracepoints

On Tue, Oct 01, 2019 at 02:08:46PM -0400, Steven Rostedt wrote:
> On Tue, 1 Oct 2019 10:42:35 -0700
> Matthias Kaehlcke <mka@...omium.org> wrote:
> 
> > 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@...omium.org> 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.
> 
> If the power management maintainers have no issues with adding these,
> then neither do I ;-)  It would be them who would pull them in anyway.

Ok, I'll send a new version with the changes you suggested and some more
info in the commit message, unless PM maintainers raise concerns before
that.