Re: [XEN RFC PATCH 07/40] xen/arm: use !CONFIG_NUMA to keep fake NUMA API

[Julien Grall <julien@xxxxxxx>]

On 20/08/2021 03:08, Wei Chen wrote:
> Hi Julien,
Hi Wei,

> > -----Original Message-----
> > From: Julien Grall <julien@xxxxxxx>
> > Sent: 2021年8月19日 21:34
> > To: Wei Chen <Wei.Chen@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> > sstabellini@xxxxxxxxxx; jbeulich@xxxxxxxx
> > Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
> > Subject: Re: [XEN RFC PATCH 07/40] xen/arm: use !CONFIG_NUMA to keep fake
> > NUMA API
> >
> > Hi Wei,
> >
> > On 11/08/2021 11:23, Wei Chen wrote:
> > > Only Arm64 supports NUMA, the CONFIG_NUMA could not be
> > > enabled for Arm32.
> > What do you mean by "could not be enabled"?
> I have not seen any Arm32 hardware support NUMA, so I think
> we don't need to support Arm32 NUMA.
I understand that there may not be 32-bit platform with NUMA. And that's 
fine stating that in the commit message. However...
> In this case, this Kconfig
> option could not be enabled on Arm32.
... you continue to say "couldn't be enabled" without clarifying whether 
this mean that the build will break or this was just not tested because 
you don't have any platform.
To put it differently, the code for NUMA looks bitness neutral. So I 
cannot really what what prevent us to potentially use it on Arm 32-bit.
> > > Even in Arm64, users still can disable
> > > the CONFIG_NUMA through Kconfig option. In this case, keep
> > > current fake NUMA API, will make Arm code still can work
> > > with NUMA aware memory allocation and scheduler.
> > >
> > > Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> > > ---
> > >    xen/include/asm-arm/numa.h | 4 ++++
> > >    1 file changed, 4 insertions(+)
> > >
> > > diff --git a/xen/include/asm-arm/numa.h b/xen/include/asm-arm/numa.h
> > > index 31a6de4e23..ab9c4a2448 100644
> > > --- a/xen/include/asm-arm/numa.h
> > > +++ b/xen/include/asm-arm/numa.h
> > > @@ -5,6 +5,8 @@
> > >
> > >    typedef u8 nodeid_t;
> > >
> > > +#if !defined(CONFIG_NUMA)
> > NIT: We tend to use #ifndef rather than #if !defined(...)
> OK, I will change related changes in this series.
>
> > > +
> > >    /* Fake one node for now. See also node_online_map. */
> > >    #define cpu_to_node(cpu) 0
> > >    #define node_to_cpumask(node)   (cpu_online_map)
> > > @@ -25,6 +27,8 @@ extern mfn_t first_valid_mfn;
> > >    #define node_start_pfn(nid) (mfn_x(first_valid_mfn))
> > >    #define __node_distance(a, b) (20)
> > >
> > > +#endif
> > > +
> > >    #endif /* __ARCH_ARM_NUMA_H */
> > >    /*
> > >     * Local variables:
> > Cheers,
> >
> > --
> > Julien Grall
Cheers,

--
Julien Grall