[refulgentis]

This doesn't shed light

Generally, any given software can be done in hardware.

Specifically, we could attach small custom coprocessors to everything for the Linux kernel, and Linux could require them to do any sort of multitasking.

In practice, software allows us to customize these things and upgrade them and change them without tightly coupling us to a specific kernel and hardware design.

[btilly]

Exactly the point. We can compile any piece of software that we want into hardware, but after that it is easier to change in software. Given the variety of unexpected ways in which hardware is used, in practice we went up moving some of what we expected to do in hardware, back into software.

This doesn't mean that moving logic into hardware can't be a win. It often is. But we should also expect that what has tended to wind up in software, will continue to do so in the future. And that includes complex decisions about the priority of interrupts.

[wizzwizz4]

We already have specialised hardware for register mapping (which could be done in software, by the compiler, but generally isn't) and resolving instruction dependency graphs (which again, could be done by a compiler). Mapping interrupts to a hardware priority level feels like the same sort of task, to me.

[sroussey]

> We already have specialised hardware for register mapping (which could be done in software, by the compiler, but generally isn't)

Wait, what? I’ve been out of compiler design for a couple decades, but that definitely used to be a thing.

[namibj]

They're probably referring to AMD Zen's speculative lifting of stack slots into physical registers (due to x86, phased out with Zen3 though), and more generally to OoO cores with far more physical than architectural registers.

[wizzwizz4]

We do register allocation in compilers, yes, but that has surprisingly little bearing on the actual microarchitectural register allocation. The priority when allocating registers these days is, iirc, avoiding false dependencies, not anything else.