Re: [PATCH v2 2/6] spapr_numa: forbid asymmetrical NUMA setups

[David Gibson]

On Fri, Sep 25, 2020 at 09:41:02AM -0300, Daniel Henrique Barboza wrote:
> 
> 
> On 9/25/20 12:48 AM, David Gibson wrote:
> > On Thu, Sep 24, 2020 at 04:50:54PM -0300, Daniel Henrique Barboza wrote:
> > > The pSeries machine does not support asymmetrical NUMA
> > > configurations. This doesn't make much of a different
> > > since we're not using user input for pSeries NUMA setup,
> > > but this will change in the next patches.
> > > 
> > > To avoid breaking existing setups, gate this change by
> > > checking for legacy NUMA support.
> > > 
> > > Reviewed-by: Greg Kurz <groug@kaod.org>
> > > Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> > 
> > Having read the rest of the series, I realized there's another type of
> > configuration that PAPR can't represent, so possibly we should add
> > logic to catch that as well.  That's what I'm going to call
> > "non-transitive" configurations, e.g.
> > 
> > Node        0       1       2
> > 0   10      20      40
> > 1   20      10      20
> > 2   40      20      10      
> > 
> > Basically the closeness of 0 to 1 and 1 to 2 forces them all to be in
> > the same domain at every PAPR level, even though 0-2 is supposed to be
> > more expensive.
> 
> Yes, this is correct. I'm not sure how to proceed in this case
> though. Should we error out?

Given that we're already erroring on asymmetric configurations, I
think it makes sense to error for these as well.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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