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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Peter Zijlstra <peterz@infradead.org>,
        Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
Cc:     Christoph Muellner <christoph.muellner@vrull.eu>,
        linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Anup Patel <apatel@ventanamicro.com>,
        Philipp Tomsich <philipp.tomsich@vrull.eu>,
        Andrew Jones <ajones@ventanamicro.com>,
        Guo Ren <guoren@kernel.org>,
        Daniel Henrique Barboza <dbarboza@ventanamicro.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@rivosinc.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
        Will Deacon <will@kernel.org>,
        Daniel Lustig <dlustig@nvidia.com>
Subject: Re: [RFC PATCH 0/5] RISC-V: Add dynamic TSO support
In-Reply-To: <20231124115430.GS3818@noisy.programming.kicks-ass.net>
References: <20231124072142.2786653-1-christoph.muellner@vrull.eu>
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 <59da3e41-abb3-405a-8f98-c74bdf26935b@huaweicloud.com>
 <20231124115430.GS3818@noisy.programming.kicks-ass.net>
Date:   Sat, 25 Nov 2023 00:05:16 +1100
Message-ID: <87plzzqp2r.fsf@mail.lhotse>
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Peter Zijlstra <peterz@infradead.org> writes:
> On Fri, Nov 24, 2023 at 12:04:09PM +0100, Jonas Oberhauser wrote:
>
>> > I think ARM64 approached this problem by adding the
>> > load-acquire/store-release instructions and for TSO based code,
>> > translate into those (eg. x86 -> arm64 transpilers).
>> 
>> 
>> Although those instructions have a bit more ordering constraints.
>> 
>> I have heard rumors that the apple chips also have a register that can be
>> set at runtime.
>
> Oh, I thought they made do with the load-acquire/store-release thingies.
> But to be fair, I haven't been paying *that* much attention to the apple
> stuff.
>
> I did read about how they fudged some of the x86 flags thing.
>
>> And there are some IBM machines that have a setting, but not sure how it is
>> controlled.
>
> Cute, I'm assuming this is the Power series (s390 already being TSO)? I
> wasn't aware they had this.

Are you referring to Strong Access Ordering? That is a per-page
attribute, not a CPU mode, and was removed in ISA v3.1 anyway.

cheers