linux-kernel - Re: [RFC 2/4] arch-topology: add a default implementation of store_cpu

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Message-ID: <YsgA/eycDF9TgCIT@kroah.com>
Date:   Fri, 8 Jul 2022 12:03:41 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Conor Dooley <Conor.Dooley@...rochip.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmer@...osinc.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Daire.McNamara@...rochip.com,
        Niklas Cassel <niklas.cassel@....com>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Zong Li <zong.li@...ive.com>,
        Emil Renner Berthing <kernel@...il.dk>, hahnjo@...njo.de,
        Guo Ren <guoren@...nel.org>, Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>, changbin.du@...el.com,
        Heiko Stuebner <heiko@...ech.de>, philipp.tomsich@...ll.eu,
        Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Brice.Goglin@...ia.fr
Subject: Re: [RFC 2/4] arch-topology: add a default implementation of
 store_cpu_topology()

On Fri, Jul 08, 2022 at 10:47:10AM +0100, Sudeep Holla wrote:
> On Fri, Jul 08, 2022 at 11:28:19AM +0200, Geert Uytterhoeven wrote:
> > Hi Sudeep,
> > 
> > On Fri, Jul 8, 2022 at 11:22 AM Sudeep Holla <sudeep.holla@....com> wrote:
> > > On Fri, Jul 08, 2022 at 08:35:57AM +0000, Conor.Dooley@...rochip.com wrote:
> > > > On 08/07/2022 09:24, Sudeep Holla wrote:
> > > > > On Thu, Jul 07, 2022 at 11:04:35PM +0100, Conor Dooley wrote:
> > > > >> From: Conor Dooley <conor.dooley@...rochip.com>
> > > > >>
> > > > >> RISC-V & arm64 both use an almost identical method of filling in
> > > > >> default vales for arch topology. Create a weakly defined default
> > > > >> implementation with the intent of migrating both archs to use it.
> > > > >>
> > > > >> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> > > > >> ---
> > > > >>   drivers/base/arch_topology.c  | 19 +++++++++++++++++++
> > > > >>   include/linux/arch_topology.h |  1 +
> > > > >>   2 files changed, 20 insertions(+)
> > > > >>
> > > > >> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> > > > >> index 441e14ac33a4..07e84c6ac5c2 100644
> > > > >> --- a/drivers/base/arch_topology.c
> > > > >> +++ b/drivers/base/arch_topology.c
> > > > >> @@ -765,6 +765,25 @@ void update_siblings_masks(unsigned int cpuid)
> > > > >>    }
> > > > >>   }
> > > > >>
> > > > >> +void __weak store_cpu_topology(unsigned int cpuid)
> > > >
> > > > Does using __weak here make sense to you?
> > > >
> > >
> > > I don't want any weak definition and arch to override as we know only
> > > arm64 and RISC-V are the only users and they are aligned to have same
> > > implementation. So weak definition doesn't make sense to me.
> > >
> > > > >
> > > > > I prefer to have this as default implementation. So just get the risc-v
> > > > > one pushed to upstream first(for v5.20) and get all the backports if required.
> > > > > Next cycle(i.e. v5.21), you can move both RISC-V and arm64.
> > > > >
> > > >
> > > > Yeah, that was my intention. I meant to label patch 1/4 as "PATCH"
> > > > and (2,3,4)/4 as RFC but forgot. I talked with Palmer about doing
> > > > the risc-v impl. and then migrate both on IRC & he seemed happy with
> > > > it.
> > > >
> > >
> > > Ah OK, good.
> > >
> > > > If you're okay with patch 1/4, I'll resubmit it as a standalone v2.
> > > >
> > >
> > > That would be great, thanks. You can most the code to move to generic from
> > > both arm64 and risc-v once we have this in v5.20-rc1
> > 
> > Why not ignore risc-v for now, and move the arm64 implementation to
> > the generic code for v5.20, so every arch will have it at once?
> >
> 
> We could but,
> 1. This arch_topology is new and has been going through lot of changes
>    recently and having code there might make it difficult to backport
>    changes that are required for RISC-V(my guess)

Worry about future issues in the future.  Make it simple now as you know
what you are dealing with at the moment.

thanks,

greg k-h