Linus> On Sun, 6 Nov 2005, John Stoffel wrote:
>>
>> Has any vendor come close to the ideal CPU architecture for an OS? I
>> would assume that you'd want:
Linus> Well, in the end, the #1 requirement ends up being "wide
Linus> availability of development boxes".
Heh! Take my thoughts and turn them on my head. Bravo!
Linus> We do want a "big enough" virtual address space, that's pretty
Linus> much required. It doesn't necessarily have to be the full 64
Linus> bits, and it's fine if the IO space is just a part of that.
So 40 bits is fine for now, but 64 would be great just because it
solves the problem for a long long time?
Linus> As to ISA and registers - nobody much cares. The compiler takes
Linus> care of it, and I'd personally _much_ rather see a common ISA
Linus> than a "clean" one. The x86 architecture may be odd, but it
Linus> works well.
But aren't there areas where the ISA would expose useful parts of the
underlying microarchitecture that could be more efficiently used in
OSes?
Linus> - fast large first-level caches help a lot. And I'd rather
Linus> take a bigger L1 that has a two- or even three-cycle latency
Linus> than a small one. That's assuming the uarch is out-of-order,
Linus> of course.
Linus> - good fast L2, and I'll take low-latency memory access over
Linus> an L3 any day.
Linus> - low-latency serialization (locking and memory barriers). In
Linus> fact, pretty much low-latency everything (branch mispredict
Linus> latency etc).
Linus> - cheap and powerful.
Linus> but the fact is, we'll work with pretty much any crap we're
Linus> given. If it's bad, it won't make it in the marketplace.
The corollary of course is that if it's excellent but the marketplace
doesn't like it for some reason, we'll still let it go. I keep
wishing for the Alpha to come back sometimes... Oh well.
Thanks for your thoughts Linus.
John
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