On Tue, Dec 01, 2020 at 09:55:22PM -0800, Alexei Starovoitov wrote: > 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. Ack, I'll drop the atomic subtract instruction.
