Re: [PATCH v2 9/9] xen: introduce a Kconfig option to configure NUMA nodes number

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 14/07/2022 12:10, Jan Beulich wrote:
> On 14.07.2022 12:14, Wei Chen wrote:
> > Hi Jan,
> >
> > > -----Original Message-----
> > > From: Jan Beulich <jbeulich@xxxxxxxx>
> > > Sent: 2022年7月12日 22:34
> > > To: Wei Chen <Wei.Chen@xxxxxxx>
> > > Cc: nd <nd@xxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; George
> > > Dunlap <george.dunlap@xxxxxxxxxx>; Julien Grall <julien@xxxxxxx>; Stefano
> > > Stabellini <sstabellini@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Roger Pau Monné
> > > <roger.pau@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > > Subject: Re: [PATCH v2 9/9] xen: introduce a Kconfig option to configure
> > > NUMA nodes number
> > >
> > > On 08.07.2022 16:54, Wei Chen wrote:
> > > > --- a/xen/arch/Kconfig
> > > > +++ b/xen/arch/Kconfig
> > > > @@ -17,3 +17,14 @@ config NR_CPUS
> > > >           For CPU cores which support Simultaneous Multi-Threading or
> > > similar
> > > >           technologies, this the number of logical threads which Xen will
> > > >           support.
> > > > +
> > > > +config NR_NUMA_NODES
> > > > +       int "Maximum number of NUMA nodes supported"
> > > > +       range 1 255
> > > > +       default "64"
> > > > +       depends on NUMA
> > > Does 1 make sense? That's not going to be NUMA then, I would say.
> > Ok, we need at least 2 nodes to be a real NUMA.
> >
> > > Does the value being (perhaps far) larger than NR_CPUS make sense?
> > Arm has 128 default NR_CPUS (except some platforms) and x86 has 256.
> > So I am not very clear about your comments about far larger? As my
> > Understanding, one node has 2 or 4 cores are very common in a NUMA
> > System.
> The defaults are fine. But does it make sense to have 255 nodes when
> just 32 CPUs were selected? I'm afraid kconfig is going to get in the
> way, but I think I'd like the upper bound to be min(NR_CPUS, 255).
Looking around NUMA nodes with 0 CPUs exists. So I don't think we should 
tie the two.
Cheers,

--
Julien Grall