Re: [RFC PATCH 0/5] RISC-V: Add dynamic TSO support

[Michael Ellerman]

Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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