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 19:29
> To: Wei Chen <Wei.Chen@arm.com>; xen-devel@lists.xenproject.org;
> sstabellini@kernel.org
> 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 11:49, Wei Chen wrote:
> > Hi Julien,
> 
> Hi Wei,
> 
> >
> >> -----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?
> 
> I think so.
> 
> >     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
> 
> Distributions should not have to build a different Xen for DT and ACPI.
> So it is more they *must* co-exist.
> 
> >     will check the system ACPI support status to decide to use
> >     DT_NUMA or ACPI_NUMA?
> 
> Yes. A user should only have to say "I want to use NUMA". This is Xen to
> figure out whether we need to compile the support for DT and/or ACPI.
> 
> Once we have support for APCI, it doesn't make a lot of sense for the
> users to say "I want to compile with DT and ACPI but I only want NUMA
> when using DT".
> 

I am glad we are now in the same page. Ok, I will change the Kconfig
like this in next version.

> Cheers,
> 
> --
> Julien Grall