I'm curious: since you're targeting Graviton, and AFAICT Graviton 2 and up support ARM LSE, have you tried directly using LSE for metrics? ARM LSE offers STADD to add to a 64-bit memory location without reading the contents or ordering the access. (I think LDADD with XZR as the destination is identical, but I could be missing some subtlety. I'm not an ARM expert.) You might be able to get good performance by using a global counter and just STADDing to it. x86 will perform terribly if you use XADD because it has no corresponding optimized forms.