Re: [Xen-devel] [RFC PATCH v3 01/24] NUMA: Make number of NUMA nodes configurable

[Julien Grall <julien.grall@xxxxxxx>]

On 19/07/17 09:17, Wei Liu wrote:
> On Tue, Jul 18, 2017 at 06:52:11PM +0100, Julien Grall wrote:
> > Hi,
> >
> > On 18/07/17 16:29, Wei Liu wrote:
> > > On Tue, Jul 18, 2017 at 05:11:23PM +0530, vijay.kilari@xxxxxxxxx wrote:
> > > > From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxx>
> > > >
> > > > Introduce NR_NODES config option to specify number
> > > > of NUMA nodes supported. By default value is set at
> > > > 64 for x86 and 8 for arm. Dropped NODES_SHIFT macro.
> > > >
> > > > Also move NR_NODE_MEMBLKS from asm-x86/acpi.h to xen/numa.h
> > > >
> > > > Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxx>
> > > > ---
> > > >  xen/arch/Kconfig           | 7 +++++++
> > > >  xen/include/asm-x86/acpi.h | 1 -
> > > >  xen/include/asm-x86/numa.h | 2 --
> > > >  xen/include/xen/config.h   | 1 +
> > > >  xen/include/xen/numa.h     | 7 ++-----
> > > >  5 files changed, 10 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
> > > > index cf0acb7..9c2a4e2 100644
> > > > --- a/xen/arch/Kconfig
> > > > +++ b/xen/arch/Kconfig
> > > > @@ -6,3 +6,10 @@ config NR_CPUS
> > > >         default "128" if ARM
> > > >         ---help---
> > > >           Specifies the maximum number of physical CPUs which Xen will support.
> > > > +
> > > > +config NR_NODES
> > > > +       int "Maximum number of NUMA nodes"
> > > > +       default "64" if X86
> > > > +       default "8" if ARM
> > > > +       ---help---
> > > > +         Specifies the maximum number of NUMA nodes which Xen will support.
> > > Since this can now be specified by user but the definition of
> > > NUMA_NO_NODE is  not changed, I think you need to sanitise the value
> > > provided somewhere.
> > >
> > > Maybe introduce a build time check? There are some examples in tree. See
> > > cpuid.c:build_assertions.
> > You can do bound-checking in Kconfig:
> >
> > range 1 254
> Oh, good to know. Yes this is the way to go.
(Not directed to you Wei :))

Actually looking again at Xen, we are moving away from a power of 2. So 
what is the rationale behind that? Have you looked at why describing the 
number of nodes in term of power of 2 was chosen?
Cheers,

--
Julien Grall

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