Re: [PATCH v10 3/6] PM / Domains: make governor select deepest state

[Axel Haslam]

Hi Zhaoyang,


> > @@ -209,14 +186,52 @@ static bool default_power_down_ok(struct dev_pm_domain *pd)
> >           * The difference between the computed minimum subdomain or device off
> >           * time and the time needed to turn the domain on is the maximum
> >           * theoretical time this domain can spend in the "off" state.
> > -        * Use the only available state, until multiple state support is added
> > -        * to the governor.
> >           */
> >          genpd->max_off_time_ns = min_off_time_ns -
> > -               genpd->states[0].power_on_latency_ns;
> > +                       genpd->states[state].power_on_latency_ns;
> >          return true;
> >   }
> [question]: Does it mean that the sleep level is just decided by
> comparing the pre-configure on_off time with the gpd_timing_data? How
> about the next timer event which affect the sleep depth on cpuidle
> framework?



There are a couple of patches on the list ill try to summarize
what i understand, Lina, Marc please correct me if im wrong!

I did this patches thinking generally about devices in a power domain 
and not so much about a cpu. So these patches are not aimed at replacing 
cpuidle, but were meant for power domains that may have intermediate 
states, for example some logic may be implemented with retention flip-flops.

There is the proposal by Lina [1] to add cpus clusters to powerdomins
and by Marc[2] that tie cluster idle states to the powerdomain handler.
but i think the effort here is to complement cpuidle rather than to
replace it.

regards
Axel

1. https://lwn.net/Articles/653579/
2. https://lwn.net/Articles/658461/

> > +static bool default_power_down_ok(struct dev_pm_domain *pd)
> > +{
> > +       struct generic_pm_domain *genpd = pd_to_genpd(pd);
> > +       unsigned int last_state_idx = genpd->state_count - 1;
> > +       struct gpd_link *link;
> > +       bool retval = false;
> > +       unsigned int i;
> > +
> > +       /*
> > +        * if there was no change on max_off_time, we can return the
> > +        * cached value and we dont need to find a new target_state
> > +        */
> > +       if (!genpd->max_off_time_changed)
> > +               return genpd->cached_power_down_ok;
> > +
> > +       /*
> > +        * We have to invalidate the cached results for the masters, so
> > +        * use the observation that default_power_down_ok() is not
> > +        * going to be called for any master until this instance
> > +        * returns.
> > +        */
> > +       list_for_each_entry(link, &genpd->slave_links, slave_node)
> > +               link->master->max_off_time_changed = true;
> > +
> > +       genpd->max_off_time_ns = -1;
> > +       genpd->max_off_time_changed = false;
> > +
> > +       /* find a state to power down to, starting from the deepest */
> > +       for (i = 0; i < genpd->state_count; i++) {
> > +               if (power_down_ok_for_state(pd, last_state_idx - i)) {
> > +                       genpd->state_idx = last_state_idx - i;
> > +                       retval = true;
> > +                       break;
> > +               }
> > +       }
> > +
> > +       genpd->cached_power_down_ok = retval;
> > +       return retval;
> > +}
> > +
> >   static bool always_on_power_down_ok(struct dev_pm_domain *domain)
> >   {
> >          return false;
> [question]How the TICK_NOHZ treated if we substitute cpuidle framework
> with this one?
> > --
> > 2.4.5
> >
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