21 ms·
That's a bit of a disingenuous exaggeration. It's not the page table walking hardware itself which is Turing complete -- it's the page fault handling mechanism
by atq2119 8y ago
That's a bit of a disingenuous exaggeration. It's not the page table walking hardware itself which is Turing complete -- it's the page fault handling mechanism as a whole, and trapcc involves playing around with trap gates and TSS from what I recall, which almost certainly involves executing microcode that goes through the main core execution units even if not a single x86 instruction is being executed.
So no, it's really not fair to say that the page table walker is its own computer. It's just a simple state machine. One tuned for high performance etc., but far from a fully-fledged computer.
- kazinator 8y agoExactly: can we have the MMU continue to execute the steps of its Turing computation (that having been configured via the trapcc program), if we clock the CPU to zero Hz? All independently identifiable and enumerable computers in a system should be capable of continuing with their computations if their clock remains running while other computers are clocked down.
- monocasa 8y agoThe cores in each core complex in my phone can't be clocked separately. Are they not cores?
- kazinator 8y agoThey can, they just aren't. Big difference. They have other ways to independently halt. Obviously any core can carry out a calculation, like calculating some arbitrarily chosen recursive primitive function, while the other cores do something completely independent, or execute a halting instruction.
- monocasa 8y agoWhat about a Niagra T1? All eight cores share a single floating point execution unit. They literally can't be clocked separately. And it's not like they're eight "cores" that are really eight SMT threads that are veneers of the same core. They are completely separate cores except the floating point unit.