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

[Vincent Guittot]

On Wed, 19 Dec 2018 at 11:43, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Wed, 19 Dec 2018 at 11:34, Vincent Guittot
> <vincent.guittot@xxxxxxxxxx> wrote:
> >
> > On Wed, 19 Dec 2018 at 11:21, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> > >

> > > > > >
> > > > > > 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().

Ok for this point if Rafael doesn't see any benefit of keeping the
generic interface

> 2. Don't allow the user of pm_runtime_accounted_time_get() to update
> the current timestamp, in "dev->power.accounting_timestamp".

But pm_runtime_accounted_time_get doesn't update
dev->power.accounting_timestamp, it only reads it to know when when
the last state transition happened

>
> Is that okay for the drm driver, to do what it does today?

drm driver needs 2 things: the  accounted suspended time since the
last transition
and the time elapse in the current state when suspened

>
> >
> > >
> > > >
> > > > >
> > > > > It seems like it should be sufficient to return the delta between
> > > > > "now" and the "dev->power.accounting_timestamp", when
> > > > > "dev->power.runtime_status == RPM_SUSPENDED".
> > > > >
> > > > > In other case, just return 0, because we are not in RPM_SUSPENDED state.
> > > >
> > > > only the RPM_SUSPENDED is used by i915/drm but wanted to provide a
> > > > generic interface to get
> > > > suspended or not suspend state
> > >
> > > I see.
> > >
> > > Although, unless Rafael thinks different, I would rather try to keep
> > > this as simple as possible and expose only what is needed and nothing
> > > more.
> >
> > I'm fine with both. Rafael ?
> >
> > >
> > > >
> > > > >
> > > > > > +       if (status == RPM_SUSPENDED)
> > > > > > +               time = dev->power.suspended_time + delta;
> > > > > > +       else
> > > > > > +               time = dev->power.active_time + delta;
> > > > > > +
> > > > > > +unlock:
> > > > > > +       spin_unlock_irqrestore(&dev->power.lock, flags);
> > > > > > +
> > > > > > +       return time;
> > > > > > +}
> > > > > > +
> > > > > >  /**
> > > > > >   * pm_runtime_deactivate_timer - Deactivate given device's suspend timer.
> > > > > >   * @dev: Device to handle.
> > > > > > diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> > > > > > index 54af4ee..86f21f9 100644
> > > > > > --- a/include/linux/pm_runtime.h
> > > > > > +++ b/include/linux/pm_runtime.h
> > > > > > @@ -113,6 +113,8 @@ static inline bool pm_runtime_is_irq_safe(struct device *dev)
> > > > > >         return dev->power.irq_safe;
> > > > > >  }
> > > > > >
> > > > > > +extern u64 pm_runtime_accounted_time_get(struct device *dev, enum rpm_status status, bool update);
> > > > > > +
> > > > > >  #else /* !CONFIG_PM */
> > > > > >
> > > > > >  static inline bool queue_pm_work(struct work_struct *work) { return false; }
> > > > > > --
> > > > > > 2.7.4
> > > > > >
> > > > >
> > > > > Kind regards
> > > > > Uffe
> > >
> > > Kind regards
> > > Uffe