> as virtual address spaces already offer exactly that in hardware at full speed
Operating system processors are pretty heavyweight, and there are lots of situations where smaller granularity protection domains are useful.
I'd also quibble with "at full speed." There is a metric shitton of complexity to implement virtual memory, with multi-level TLBs, an extremely careful dance with the operating system currently, IPIs for TLB shootdown, etc. The dynamic cost of the TLB is something that is measurable, and of course, completely depends on your application behavior, kernel, availability of huge pages, etc.
The reality is that we don't really have a control group for hardware without virtual memory because the only such chips are for small embedded (niche) systems, and everything else runs on kernels designed to offer virtual memory to software expecting virtual memory.
Operating system processors are pretty heavyweight, and there are lots of situations where smaller granularity protection domains are useful.
I'd also quibble with "at full speed." There is a metric shitton of complexity to implement virtual memory, with multi-level TLBs, an extremely careful dance with the operating system currently, IPIs for TLB shootdown, etc. The dynamic cost of the TLB is something that is measurable, and of course, completely depends on your application behavior, kernel, availability of huge pages, etc.
The reality is that we don't really have a control group for hardware without virtual memory because the only such chips are for small embedded (niche) systems, and everything else runs on kernels designed to offer virtual memory to software expecting virtual memory.