# Re: \[PATCH 2/3\] powerpc/numa: Populate distance map correctly

- From: Srikar Dronamraju \<hidden\>
- Date: 2021-05-24 14:56:30 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/05/1389591
- Thread: https://ratatoskr.run/linuxppc-dev/2021/05/1386294/t.md

```text
* Valentin Schneider [ref] [2021-05-24 15:16:22]:

> On 20/05/21 21:14, Srikar Dronamraju wrote:
> > +int arch_populate_distance_map(unsigned long *distance_map)
> > +{
> > +	int i;
> > +	int distance = LOCAL_DISTANCE;
> > +
> > +	bitmap_set(distance_map, distance, 1);
> > +
> > +	if (!form1_affinity) {
> > +		bitmap_set(distance_map, REMOTE_DISTANCE, 1);
> > +		return 0;
> > +	}
> > +
> > +	for (i = 0; i < distance_ref_points_depth; i++) {
> > +		distance *= 2;
> > +		bitmap_set(distance_map, distance, 1);
> 
> Do you have guarantees your distance values will always be in the form of
> 
>   LOCAL_DISTANCE * 2^i
> 
> because that certainly isn't true for x86/arm64.
> 

This is true till now. It don't think that's going to change anytime soon, but
we never know what lies ahead.

For all practical purposes, (unless a newer, shinier property is proposed,)
distance_ref_points_depth is going to give us the unique distances.

> > +	}
> > +	return 0;
> > +}
> > +
> >  /*
> >   * Returns nid in the range [0..nr_node_ids], or -1 if no useful NUMA
> >   * info is found.
> > --
> > 2.27.0

-- 
Thanks and Regards
Srikar Dronamraju
```