[rescue] SS10/20 death

[dave at cca.org]

mcguire at neurotica.com writes:

>  Register spilling does cause complications and performance
>problems...which is why one strives to avoid it whenever possible.
>Deep call stacks are best avoided on SPARCs...if you're within the
>depth of the register windows, you're in good shape and things fly.
>If you spill, you slow down quite a bit.  It can be looked at in the
>same manner as caching but at a lower level...there's a bit of very
>high-speed local storage that, if your data access patterns are
>tailored to take advantage of it, will be used more heavily, reducing
>access to the next level of larger/slower storage.

What's the window depth on recent Ultrasparcs?

>> Have you ever enocuntered anyone using the windows for anything
>> other than function calls?

>  Not yet, though it might be interesting for context switching and
>possibly interprocess communication stuff.

Ah, I can see a great use it someone wants to port RT-11... :-)

>> SPARC's register windows always seemed like one of the weird &
>> abandoned experiments in the crazy early days of the "RISC hype" before
>> a few years of actually producing machines made it obvious that the
>> wins of "RISC" amounted to: load/store arch & fixed length instructions.
>> (Which is why I still think Cray's machines qualify, all the way back
>> to the CDC-6600.)

>  It's not abandoned at all.  All SPARCs, including UltraSPARCs, use
>register windowing.  I've heard that several other (now
>non-mainstream) processors have but I can't think of any off the top
>of my head.

No no, I meant it sounds *like* one of those weird experiments that
was abondoned, but actually, it wasn't.

What's that RISC CPU that comes crammed into the corner of a chip, and
you get the rest of the real estate as your own ASIC?  29000 perhaps?
Did that have register windows?

Some othe CPU had register windows that didn't move a fixed number of
registers.

>  And yes, many early computer architectures qualify as RISC by today's
>definitions.  That's why I always preach to people about the
>importance of studying the TRUE beginnings of computers.

*Why* does CS continue to be the discipline that ignores history?
It's been notorious for that for most of its existance, yet the
situation never changes...

------ David Fischer ------- dave at cca.org ------- http://www.cca.org ------
----------------- Live each day like the Triffids are coming. -------------