Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub

[Alexei Starovoitov]

On Tue, Dec 1, 2020 at 4:38 AM Brendan Jackman <jackmanb@xxxxxxxxxx> wrote:
>
> I guess it's also worth remembering other archs might have an atomic
> subtract.

which one?
arm64 LSE implements atomic_fetch_sub as neg+ldadd.
imo x64 and arm64 example outweighs choices by other archs if there are such.
Even without LSE it will be neg+llsc loop.
The reason I proposed bpf xsub insn earlier is that I thought that llvm
won't be able to emit it so easily and JIT/verifier would struggle.