On Sun, Sep 27, 2020 at 08:41:30AM -0300, Daniel Henrique Barboza wrote: > > > On 9/26/20 4:49 AM, David Gibson wrote: > > 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 <gr...@kaod.org> > > > > > Signed-off-by: Daniel Henrique Barboza <danielhb...@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. > > Thing is that asymmetrical configurations is an easy concept to enforce > to the user - distance from A to B can't be different from B to A. > > In the example you gave above, with 3 NUMA nodes, is easy to spot where > the non-transitivity rule would hit. I'm afraid that if we add 2-3 more > NUMA nodes in the mix this will stop being straightforward, with more and > more combinations hitting the 'non-transitivity' rule, and erroring out > will end up being frustrating to the user. > > I'd say that we should report this in the documentation as one more > limitation of the implementation (and PAPR). I wouldn't oppose with > throwing a warning message either, letting the user know that the > approximation will be less precise than it already would be in this > case.
Hmm... yes, I see your point. Ok, let's go with your suggestion.
--
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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