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0 pointschrismonsanto6y ago0 comments

> in practice

FWIW RISC-V guarantees forward progress for reasonable uses:

> We mandate that LR/SC sequences of bounded length (16 consecutive static instructions) will eventually succeed, provided they contain only base ISA instructions other than loads, stores, and taken branches.

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gpderetta6y ago

[sorry for the late reply]

what happens if those 16 instructions touch 16 different cache lines? I'm not an hardware expert (and even less on coherency protocols), but I think it would be extremely hard to make sure livelocking is avoided in all cases, short of having some extremely expensive and heavy handed global 'bus' lock fallback.

chrismonsantoOP6y ago

Reading and writing memory are excluded from the guarantee, aside from the LR/SC instructions that bookend a transaction. Inside the transaction you're basically limited to register-register ALU and aborting branches.

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