3 ms·

It is worth noting that many of the Mill features are also a "lie" (for example, the belt is still just registers and register renaming). Its just that the Mill

It is worth noting that many of the Mill features are also a "lie" (for example, the belt is still just registers and register renaming). Its just that the Mill uses lies designed for modern processor technology.

w0000t 11y ago
False. Mill does not do register renaming. ( Or use "lies". I failed to comprehend you second sentence. ) Here is a talk from one of the designers explaining how it is done: https://www.youtube.com/watch?v=QGw-cy0ylCc&feature=youtu.be&t=24m38s https://www.youtube.com/watch?v=QGw-cy0ylCc&feature=youtu.be...
- stdbrouw 11y ago
  "Lie" in this context means something like "abstraction or metaphor that doesn't present itself as such."
zurn 11y ago
Yes, registers and the belt are just ISA features. Register renaming is a behind the scenes implementation tech to mitigate the problems of register semantics. It has unwanted costs that a belt machine doesn't have to pay, and it's incorrect to say that Mill does register renaming in the traditional sense of the word. Indeed that's what the #1 paragraph at https://millcomputing.com/docs/belt/ https://millcomputing.com/docs/belt/ says: "A large fraction of the power budget of modern superscalar CPUs is devoted to renaming registers: the CPU must track the dataflow of the executing program, assign physical registers and map them to the logical registers of the program, schedule operations when arguments are available, restore visible state in the event of an exception—all while avoiding register update hazards."
Symmetry 11y ago
The belt isn't an abstraction of the structures in a modern OoO CPU corresponding to registers and renaming but rather the bypass network further down the pipeline. The belt like the bypass network only has to store data for limited periods and the translation is much simpler than what an OoO CPU has to do when renaming registers.

w0000t 11y ago

False. Mill does not do register renaming. ( Or use "lies". I failed to comprehend you second sentence. ) Here is a talk from one of the designers explaining how it is done: https://www.youtube.com/watch?v=QGw-cy0ylCc&feature=youtu.be&t=24m38s https://www.youtube.com/watch?v=QGw-cy0ylCc&feature=youtu.be...

stdbrouw 11y ago
"Lie" in this context means something like "abstraction or metaphor that doesn't present itself as such."

zurn 11y ago

Yes, registers and the belt are just ISA features. Register renaming is a behind the scenes implementation tech to mitigate the problems of register semantics. It has unwanted costs that a belt machine doesn't have to pay, and it's incorrect to say that Mill does register renaming in the traditional sense of the word. Indeed that's what the #1 paragraph at https://millcomputing.com/docs/belt/ https://millcomputing.com/docs/belt/ says: "A large fraction of the power budget of modern superscalar CPUs is devoted to renaming registers: the CPU must track the dataflow of the executing program, assign physical registers and map them to the logical registers of the program, schedule operations when arguments are available, restore visible state in the event of an exception—all while avoiding register update hazards."

Symmetry 11y ago

The belt isn't an abstraction of the structures in a modern OoO CPU corresponding to registers and renaming but rather the bypass network further down the pipeline. The belt like the bypass network only has to store data for limited periods and the translation is much simpler than what an OoO CPU has to do when renaming registers.