Re: [Qemu-devel] [Qemu-ppc] [PATCH for 2.13] spapr: Correct max associativity domains value for non-NUMA configs

[Greg Kurz <groug@kaod.org>]

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On Wed, 18 Apr 2018 11:49:08 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Tue, Apr 17, 2018 at 07:17:51PM +0200, Greg Kurz wrote:
> > Cc'ing David who should always be in the recipient list when posting ppc related
> > patches :)
> > 
> > On Tue, 17 Apr 2018 12:21:35 -0400
> > Serhii Popovych <spopovyc@redhat.com> wrote:
> >   
> > > In non-NUMA configurations nb_numa_nodes is zero and we set 5th cell
> > > in ibm,max-associativity-domains to -1. That causes to stall Linux
> > > guests during boot after following line:
> > > 
> > > [    0.000000] NUMA associativity depth for CPU/Memory: 4
> > > 
> > > Make last possible NUMA in property zero to correct support for
> > > non-NUMA guests.
> > >   
> > 
> > Alternatively, as suggested by David in some other mail, you could drop the
> > property in this case. I've checked it fixes the hang too, and it probably
> > makes more sense than exposing only zeroes.  
> 
> Actually, I think this is the better solution. qemu treats "not NUMA"
> and "exactly one NUMA node" differently for historical reasons, but I
> don't think that actually makes a whole lot of sense.  I think
> advertising them identically so we don't generate more special cases
> on the guest side is a better idea.
> 

Fair enough. Thanks for the explanation.

> > > Fixes: c1df49a670ef ("spapr: Add ibm,max-associativity-domains property")  
> > 
> > Since c1df49a670ef hasn't hit master yet, I guess we should squash this
> > patch (or any alternative) there to preserve bisect, ie, either David
> > does it for you or you post a v4 of your previous series.  
> 
> Right, I've folded these together in my tree so we don't get an
> interval of broken commits.
> 
> >   
> > > Signed-off-by: Serhii Popovych <spopovyc@redhat.com>
> > > ---
> > >  hw/ppc/spapr.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index 7b2bc4e..bff2125 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -914,7 +914,7 @@ static void spapr_dt_rtas(sPAPRMachineState *spapr, void *fdt)
> > >          cpu_to_be32(0),
> > >          cpu_to_be32(0),
> > >          cpu_to_be32(0),
> > > -        cpu_to_be32(nb_numa_nodes - 1),
> > > +        cpu_to_be32(nb_numa_nodes ? nb_numa_nodes - 1 : 0),
> > >      };
> > >  
> > >      _FDT(rtas = fdt_add_subnode(fdt, 0, "rtas"));  
> > 
> >   
> 


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