Re: [RFCv3 PATCH 30/48] sched: Calculate energy consumption of sched_group

[Morten Rasmussen]

On Tue, Mar 24, 2015 at 04:10:37PM +0000, Peter Zijlstra wrote:
> On Tue, Mar 24, 2015 at 10:44:24AM +0000, Morten Rasmussen wrote:
> > > > Maybe remind us why this needs to be tied to sched_groups ? Why can't we
> > > > attach the energy information to the domains?
> 
> > In the current domain hierarchy you don't have domains with just one cpu
> > in them. If you attach the per-cpu energy data to the MC level domain
> > which spans the whole cluster, you break the current idea of attaching
> > information to the cpumask (currently sched_group, but could be
> > sched_domain as we discuss here) the information is associated with. You
> > would have to either introduce a level of single cpu domains at the
> > lowest level or move away from the idea of attaching data to the cpumask
> > that is associated with it.
> > 
> > Using sched_groups we do already have single cpu groups that we can
> > attach per-cpu data to, but we are missing a top level group spanning
> > the entire system for system wide energy data. So from that point of
> > view groups and domains are equally bad.
> 
> Oh urgh, good point that. Cursed if you do, cursed if you don't. Bugger.

Yeah :( I don't really care which one we choose. Adding another top
level domain with one big group spanning all cpus, but with all SD flags
disabled seems less intrusive than adding a level at the bottom.

Better ideas are very welcome.
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