Claire Xen  🏳️‍⚧️ 🏳️‍🌈 🧙🏻‍♀️ BLM  🏴 🚩

Roughly half is moderately serious, half is pointless pedantry about things that don't matter or complaints about good choices.

Atomics being optional is absolutely wrong. Non-SMP core can implement lr/sc trivially and should be required to. Likewise for mul but not quite as serious since it *can* be emulated in sw.

I disagree. Platform specs require A where it makes sense (such as Linux). There's nothing to gain from forcing tiny embedded cores for inherently non-smp platforms to implement mockup atomics.

They're necessary to implement synchronization between tasks, which is potentially useful in software on such cores, without a global sw ("kernel") helper. And the amount of logic needed for non-SMP implementation is utterly trivial.

There's nothing you'd need atomics for on an inherently non-smp platform. No matter how trivial the implementation would be, there's no reason to include it on non-smp platforms. Platform specs for platforms that may come in smp variants will certainly require A instructions.

Yes there is. Atomics are just as important for non-SMP, to implement synchronization between tasks. Otherwise you need complex restart protocol mediated by scheduler.

With non-smp platforms I mean platforms with only one core, not non-symmetric multicore platforms. Sorry, I should have been more clear. Let me rephrase: For platforms on which atomics make any sense whatsoever, the platform spec will require atomics.

I'm not talking about non-symmetric MP. Pure single core. Atomics are absolutely needed there to implement multitasking without a kernel scheduler doing custom restart sequence mediation.