Re: [tip:sched/core] sched/numa: Rewrite the CONFIG_NUMA sched domain support

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Wed, 2012-06-06 at 15:43 +0800, Alex Shi wrote:
> > +       /*
> > +        * O(nr_nodes^2) deduplicating selection sort -- in order to find the
> > +        * unique distances in the node_distance() table.
> > +        *
> > +        * Assumes node_distance(0,j) includes all distances in
> > +        * node_distance(i,j) in order to avoid cubic time.
> 
> Curious for other platforms node_distance number, actually, this
> assumption is right for what I saw Intel platforms. but it is not
> match acpispec50.pdf:
> 
> Table 6-152 Example Relative Distances Between Proximity Domains
> Proximity Domain 0 1 2 3
> 0 10 15 20 18
> 1 15 10 16 24
> 2 20 16 10 12
> 3 18 24 12 10

Yes I know its allowed, I just haven't seen it in practice.

I've got a patch that validates this assumption if you boot with
"sched_debug". If we ever run into such a setup we might need to fix
this -- it shouldn't be too hard, just expensive.