Re: Best CPU chipset for Linux? (was: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19)

["John Stoffel" <john@stoffel.org>]

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