Linus Torvalds (torvalds@linux-foundation.org) on 6/21/08 wrote:
---------------------------
>S. Rao (sonny@burdell.org) on 6/21/08 wrote:
>>
>>(Maybe I'm way off here, but here goes)
>>
>>Remember that thing called register renaming ?
>>
>>Why does the architected register File have anything to
>>do with it?
>
>You want to rename into a larger set of physical
>registers, not into a smaller one. The latter is possible
>but very very inconvenient (it is what you effectively
>have to do if you are emulating a large register file
>architecture on a CPU with a smaller register file: you
>map the large register file into cache or some other
>"secondary" register file, and then rename it all into the
>smaller actual register file).
>
>So even with renaming, you do care about the size of the
>architected register file. A smaller architected register
>file allows you more flexibility in choosing the size of
>the actual hardware register file.

I think the implementation will make a difference here,
if you keep your architected state in the physical reg
file then yeah more threads == fewer renames. I think
IBM does it this way but not sure if Intel does it
this way necessarily. But then I would say you have
to weight it againt the penalty you're paying for having
fewer regs in the first place.... it's not clear that it
isn't a wash when it comes to complexity/timing