It’s not necessary to serialize the full execution to detect errors. On an out of order processor, there is already buffering of results happening that is event

It’s not necessary to serialize the full execution to detect errors. On an out of order processor, there is already buffering of results happening that is eventually serialized to visible state. To check errors, you could just have one buffer per processor and compare results before serialization, raising an error on mismatch between processors. Serialization is merely indicating that both _visible_ executions have agreed up to that instruction but it still allows for some local/internal disagreements. For example, two instructions can finish in opposite orders across cores and that is fine as long as they are serialized in order. As for settling times, those are random anyway. Processors are binned according to how good the settling times ended up being. It’s unlikely to have two homogeneous chips.