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From:   Linus Torvalds <torvalds@linuxfoundation.org>
Date:   Tue, 28 Feb 2023 17:07:11 -0800
Message-ID: <CAHk-=wiGA91ca02-J0ebAnCE1wA_=Q35MiFz4ONo3Zw76uFxNQ@mail.gmail.com>
Subject: Re: [patch 2/3] atomics: Provide rcuref - scalable reference counting
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Wangyang Guo <wangyang.guo@intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Marc Zyngier <maz@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org
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On Tue, Feb 28, 2023 at 4:42=E2=80=AFPM Linus Torvalds
<torvalds@linuxfoundation.org> wrote:
>
> And yes, that may mean that it should have some architecture-specific
> code (with fallback defaults for the generic case).

Another reason for architecture-specific code is that anybody who
doesn't have atomics and just relies on an LL/SC model is actually
better of *not* having any of this complexity.

In fact, the Intel RAO instruction set would likely do that on x86
too. With that alleged future "CMPccXADD", there likely is no longer
any advantage to this model of rcuref.

Now, I don't know when - if ever - said RAO instruction set extension
comes, but I'd hope that the new scalable reference counting would be
ready for it.

             Linus