linux-kernel - Re: [RFC v3 1/3] PM/runtime: Add a new interface to get accounted time

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Message-ID: <CAPDyKFpfDF_7ZyhRY-jfapjuQQ=5KpQt7QV2-d_a-qki=omAYA@mail.gmail.com>
Date:   Wed, 19 Dec 2018 11:52:39 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        jani.nikula@...ux.intel.com,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        rodrigo.vivi@...el.com, David Airlie <airlied@...ux.ie>,
        "Intel graphics driver community testing & development" 
        <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC v3 1/3] PM/runtime: Add a new interface to get accounted time

On Wed, 19 Dec 2018 at 11:43, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Wed, 19 Dec 2018 at 11:34, Vincent Guittot
> <vincent.guittot@...aro.org> wrote:
> >
> > On Wed, 19 Dec 2018 at 11:21, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > >
> > > On Wed, 19 Dec 2018 at 11:11, Vincent Guittot
> > > <vincent.guittot@...aro.org> wrote:
> > > >
> > > > On Wed, 19 Dec 2018 at 10:58, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > > > >
> > > > > On Tue, 18 Dec 2018 at 15:55, Vincent Guittot
> > > > > <vincent.guittot@...aro.org> wrote:
> > > > > >
> > > > > > Some drivers (like i915/drm) need to get the accounted suspended time.
> > > > > > pm_runtime_accounted_time_get() will return the suspended or active
> > > > > > accounted time until now.
> > > > >
> > > > > I suggest to leave the active accounted time out for now. At least
> > > > > until we have some users.
> > > >
> > > > This is needed to keep same feature level for i915/drm
> > >
> > > I don't follow. According to the changes in the drm driver in patch2,
> > > we are only calling the new pm_runtime interface with RPM_SUSPENDED?
> >
> > sorry I mix your question above and the one about  accounting_timestamp.
> >
> > So I agree that only RPM_SUSPENDED is used for now
> >
> > >
> > > >
> > > > >
> > > > > That said, perhaps rename the function to something along the lines
> > > > > of, pm_runtime_last_suspended_time(), to make it more clear.
> > > > >
> > > > > >
> > > > > > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > > > > > ---
> > > > > >  drivers/base/power/runtime.c | 26 ++++++++++++++++++++++++++
> > > > > >  include/linux/pm_runtime.h   |  2 ++
> > > > > >  2 files changed, 28 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> > > > > > index 7062469..6461469 100644
> > > > > > --- a/drivers/base/power/runtime.c
> > > > > > +++ b/drivers/base/power/runtime.c
> > > > > > @@ -88,6 +88,32 @@ static void __update_runtime_status(struct device *dev, enum rpm_status status)
> > > > > >         dev->power.runtime_status = status;
> > > > > >  }
> > > > > >
> > > > > > +u64 pm_runtime_accounted_time_get(struct device *dev, enum rpm_status status, bool update)
> > > > > > +{
> > > > > > +       u64 now = ktime_to_ns(ktime_get());
> > > > >
> > > > > I think you should stay on jiffies here - and then switch to ktime in patch 3.
> > > > >
> > > > > > +       u64 delta = 0, time = 0;
> > > > > > +       unsigned long flags;
> > > > > > +
> > > > > > +       spin_lock_irqsave(&dev->power.lock, flags);
> > > > > > +
> > > > > > +       if (dev->power.disable_depth > 0)
> > > > > > +               goto unlock;
> > > > > > +
> > > > > > +       /* Add ongoing state  if requested */
> > > > > > +       if (update && dev->power.runtime_status == status)
> > > > > > +               delta = now - dev->power.accounting_timestamp;
> > > > > > +
> > > > >
> > > > > Hmm. Do we really need to update the accounting timestamp? I would
> > > > > rather avoid it if possible.
> > > >
> > > > i915/drm uses this to track ongoing suspended state. In fact they are
> > > > mainly interested by this part
> > >
> > > Again, sorry I don't follow.
> >
> > In fact we don't update dev->power.accounting_timestamp but only use
> > it to get how much time has elapsed in the current state.
> >
> > >
> > > My suggested changes below, would do exactly that; track the ongoing
> > > suspended state.
> > >
> > > The user can call the function several times while the device remains
> > > RPM_SUSPENDED, and if needed the user could then compute the delta
> > > in-between the calls, for whatever reason that may be needed.
> >
> > So I'm not sure to catch your question:
> > Is your problem linked to status != RPM_SUSPENDED or the update
> > parameter that compute delta ?
>
> My intent was to keep things simple.
>
> 1. Only expose last suspended time, which means tracking the ongoing
> suspended state. In other words, you can also remove "enum rpm_status
> status" as the in-parameter to pm_runtime_accounted_time_get().
> 2. Don't allow the user of pm_runtime_accounted_time_get() to update
> the current timestamp, in "dev->power.accounting_timestamp".
>
> Is that okay for the drm driver, to do what it does today?

Hold on. I am wondering if the drm driver could use the existing
pm_runtime_autosuspend_expiration() function instead. Isn't that
really that what is needed?

[...]

Kind regards
Uffe