RE: [XEN RFC PATCH 36/40] xen/arm: keep guest still be NUMA unware

[Wei Chen <Wei.Chen@arm.com>]

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: 2021年8月27日 22:28
> To: Wei Chen <Wei.Chen@arm.com>; xen-devel@lists.xenproject.org;
> sstabellini@kernel.org; jbeulich@suse.com
> Cc: Bertrand Marquis <Bertrand.Marquis@arm.com>
> Subject: Re: [XEN RFC PATCH 36/40] xen/arm: keep guest still be NUMA
> unware
> 
> Hi Wei,
> 
> On 11/08/2021 11:24, Wei Chen wrote:
> > We have not wanted to make Xen guest be NUMA aware in this patch
> > series.
> 
> The concept of patch series ceases to exist once we merge the code. So
> about how:
> 
> "The NUMA information provided in the host Device-Tree are only for Xen.
> For dom0, we want to hide them as they may be different (for now, dom0
> is still not aware of NUMA".
> 

Thanks, I will do it.

> > So in this patch, Xen will skip NUMA distance matrix node
> > and skip the numa-node-id property in CPU node and memory node,
> > when Xen is creating guest device tree binary.
> 
> The CPU and memory nodes are recreated from scratch for the domain. So
> we already skip the property numa-node-id. However...
> 
> > Signed-off-by: Wei Chen <wei.chen@arm.com>
> > ---
> >   xen/arch/arm/domain_build.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > index cf341f349f..e62fa761bd 100644
> > --- a/xen/arch/arm/domain_build.c
> > +++ b/xen/arch/arm/domain_build.c
> > @@ -584,6 +584,10 @@ static int __init write_properties(struct domain *d,
> struct kernel_info *kinfo,
> >                   continue;
> >           }
> >
> > +        /* Guest is numa unaware in current stage */
> > +        if ( dt_property_name_is_equal(prop, "numa-node-id") )
> > +            continue;
> 
> ... your code is doing more than skipping the property for the two nodes
> you mentionned. Can the property exists in other nodes?

Some devices like PCIe may have numa-node-id. In the future maybe more
device can have NUMA property.

> 
> > +
> >           res = fdt_property(kinfo->fdt, prop->name, prop_data,
> prop_len);
> >
> >           if ( res )
> > @@ -1454,6 +1458,8 @@ static int __init handle_node(struct domain *d,
> struct kernel_info *kinfo,
> >           DT_MATCH_TYPE("memory"),
> >           /* The memory mapped timer is not supported by Xen. */
> >           DT_MATCH_COMPATIBLE("arm,armv7-timer-mem"),
> > +        /* Numa info doesn't need to be exposed to Domain-0 */
> > +        DT_MATCH_COMPATIBLE("numa-distance-map-v1"),
> >           { /* sentinel */ },
> >       };
> >       static const struct dt_device_match timer_matches[] __initconst =
> >
> 
> Cheers,
> 
> --
> Julien Grall