I wish they included rust benchmark code so we can play around and improve it. If the issue really is the bounds checks, then there are many ways to massage Rust code to make it obvious they're not needed. But it seems you can't really play with it without running on actual hardware.
Really no point to running it without real hardware, it will perform completely differently if you don't have the MMIO accesses and DMA by the NIC in there.
We'll have a VirtIO driver soon, but that's bottlenecked by the hypervisor and not really useful for performance tests.
With fake memory mapping it would not access the same memory, but you'd still run the same code, right? So the timing/details of access may change a lot, but the profile of executed code would be still meaningful. For example, if you run a loop with range checks, and a loop without them, it doesn't matter what's happening in the loop, as long as it stays consistent between the runs - you can still tell things about the loop overhead.
Would need a somewhat realistic emulation of the NIC setting/clearing these flags. Also, the by far slowest steps are the MMIO access because it involves a full PCIe round trip which is hard to emulate.
It will behave different at the level we are looking at here. It's easier to use real hardware; we specifically chose this NIC because it's probably the most common 10G NIC on servers.
