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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Tue, 21 Sep 2021 14:06:24 +0200
Message-ID: <CAMj1kXGPcHwdSjy-doB09LBLvrXtqYT4dyxE5hU=D=2m8Fg8zg@mail.gmail.com>
Subject: Re: [RFC PATCH 0/8] Move task_struct::cpu back into thread_info
To:     Mark Rutland <mark.rutland@arm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <hca@linux.ibm.com>,
        Paul Mackerras <paulus@samba.org>,
        Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Keith Packard <keithpac@amazon.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@lists.ozlabs.org>,
        linux-riscv <linux-riscv@lists.infradead.org>,
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On Tue, 14 Sept 2021 at 15:55, Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Tue, Sep 14, 2021 at 02:10:28PM +0200, Ard Biesheuvel wrote:
> > Commit c65eacbe290b ("sched/core: Allow putting thread_info into
> > task_struct") mentions that, along with moving thread_info into
> > task_struct, the cpu field is moved out of the former into the latter,
> > but does not explain why.
>
> From what I recall of talking to Andy around that time, when converting
> arm64 over, the theory was that over time we'd move more and more out of
> thread_info and into task_struct or thread_struct, until task_struct
> supplanted thread_info entirely, and that all became generic.
>
> I think the key gain there was making things more *generic*, and there
> are other ways we could do that in future without moving more into
> task_struct (e.g. with a geenric thread_info and arch_thread_info inside
> that).
>
> With that in mind, and given the diffstat, I think this is worthwhile.
>
> FWIW, for the series:
>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
>

Thanks.

Any comments on this from the various arch maintainers? Especially
power, as Christophe seems happy with this but there are 3 different
patches affecting power that need a maintainer ack.