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

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Fri, 6 Nov 2015 21:55:49 +0000
Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:

> > 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.
what is WFI?
For Intel, idle states are hints to the HW. The FW decides how far the
idle can go based on many factors, device states included, some are
visible to the OS some are not. We just to help mature such deep idle
conditions.