Re: [RFC PATCH 0/3] CFS idle injection

[Dietmar Eggemann]

On 11/06/2015 07:10 PM, Jacob Pan wrote:
> On Fri, 6 Nov 2015 18:30:01 +0000
> Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
>
> > On 05/11/15 10:12, Peter Zijlstra wrote:
> > > People, trim your emails!
> > >
> > > On Wed, Nov 04, 2015 at 08:58:30AM -0800, Jacob Pan wrote:
> > >
> > > > > I also like #2 too. Specially now that it is not limited to a
> > > > > specific platform. One question though, could you still keep the
> > > > > cooling device support of it? In some systems, it might make
> > > > > sense to enable / disable idle injections based on temperature.
> > >
> > > > One of the key difference between 1 and 2 is that #2 is open loop
> > > > control, since we don't have CPU c-states info baked into
> > > > scheduler.
> > >
> > > _yet_, there's people working on that. The whole power aware
> > > scheduling stuff needs that.
> >
> > Isn't the idle state information (rq->idle_state) already used in
> > find_idlest_cpu()?
> >
> > What we use in energy aware scheduling is quite similar but since
> > we're interested in the index information of the c-state (to access
> > the right element of the idle_state vectors of the energy model, we
> > added rq->idle_state_idx.
> what i am interested is not per cpu idle state but rather at the package
> level or domain. It must be an indication for the overlapped idle time.
> Usually has to come from HW counters.

I see. We have a similar problem with the Energy Model (EM) on cluster 
level (sched domain level DIE). We iterate over the cpus of a sched 
group and declare the shallowest cpu idle state as the cluster idle 
state to index our EM. On a typical ARM system we have (active, WFI, 
cpu-off and cluster-off). But I guess for you the idle state index is 
only for core idle states and you can't draw any conclusions from this 
for the package idle states.

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