RE: [XEN RFC PATCH 17/40] xen/arm: Introduce DEVICE_TREE_NUMA Kconfig for arm64

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

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien@xen.org>
> Sent: 2021年8月20日 16:41
> 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 17/40] xen/arm: Introduce DEVICE_TREE_NUMA
> Kconfig for arm64
> 
> On 20/08/2021 03:30, Wei Chen wrote:
> > Hi Julien,
> 
> Hi Wei,
> 
> >> -----Original Message-----
> >> From: Julien Grall <julien@xen.org>
> >> Sent: 2021年8月19日 21:38
> >> 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 17/40] xen/arm: Introduce DEVICE_TREE_NUMA
> >> Kconfig for arm64
> >>
> >> Hi,
> >>
> >> On 11/08/2021 11:24, Wei Chen wrote:
> >>> We need a Kconfig option to distinguish with ACPI based
> >>> NUMA. So we introduce the new Kconfig option:
> >>> DEVICE_TREE_NUMA in this patch for Arm64.
> >>>
> >>> Signed-off-by: Wei Chen <wei.chen@arm.com>
> >>> ---
> >>>    xen/arch/arm/Kconfig | 10 ++++++++++
> >>>    1 file changed, 10 insertions(+)
> >>>
> >>> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> >>> index ecfa6822e4..678cc98ea3 100644
> >>> --- a/xen/arch/arm/Kconfig
> >>> +++ b/xen/arch/arm/Kconfig
> >>> @@ -33,6 +33,16 @@ config ACPI
> >>>    	  Advanced Configuration and Power Interface (ACPI) support
> for Xen
> >> is
> >>>    	  an alternative to device tree on ARM64.
> >>>
> >>> +config DEVICE_TREE_NUMA
> >>
> >> The name suggests that NUMA should only be enabled for Device-Tree...
> >> But the description looks generic.
> >>
> >> However, I think the user should only have the choice to say whether
> >> they want NUMA to be enabled or not. We should not give them the choice
> >> to enable/disable the parsing for DT/ACPI.
> >>
> >> So we should have a generic config that will then select DT (and ACPI
> in
> >> the future).
> >>
> >
> > How about we select DT_NUMA default on Arm64. And DT_NUMA select NUMA
> > like what we have done in patch#6 in x86? And remove the description?
> I would rather not make NUMA supported by default on Arm64. Instead, we
> should go throught the same process as other new features and gate it
> behind UNSUPPORTED until it is mature enough.
> 

Ok. I agree with this.

> >
> > If we make generic NUMA as a selectable option, and depends on
> > NUMA to select DT or ACPI NUMA. It seems to be quite different from
> > the existing logic?
> 
> I am a bit confused. You added just logic to select NUMA from ACPI,
> right? So are you talking about a different logic?
> 

No, I didn't want a different one. I thought you wanted it that way.
Obviously, I mis-understanded your comments.

Can I understand your previous comments like following:
1. We should have a generic config that will then select DT and ACPI:
   Because we already have CONFIG_NUMA in common layer. So we need to
   add another one for Arm like CONFIG_ARM_NUMA?
   And in this option, we can select CONFIG_DEVICE_TREE_NUMA
   automatically if device tree is enabled. If CONFIG_ACPI
   is enabled, we will select CONFIG_ACPI_NUMA too (in the
   future)
   In Xen code, DT_NUMA and ACPI_NUMA code can co-exist, Xen
   will check the system ACPI support status to decide to use
   DT_NUMA or ACPI_NUMA?


> Cheers,
> 
> --
> Julien Grall