[Beowulf] Three notes from ISC 2006

Mark Hahn hahn at physics.mcmaster.ca
Wed Jun 28 21:44:41 EDT 2006


> a huge L3 cache (which most specfp software is somehow) that it destroyed 

spec is, after all, CPU2000, and things have changed quite a lot in 6+ years.
Itaniums were one of the earliest "breaks" of spec cpu2000 codes,
(besides sun's spec-special compiler).  if you take it2 results 
and remove the ~2 smallest-memory components, you get less impressed.
I think this has a lot to do with it2's trajectory.

it'll be interesting to see how much of Core2's performance is due to 
the big 4M shared onchip L2 - Intel doesn't seem to have any 2M scores
on spec.org yet.

> So getting a 20% higher IPC there than k8 is quite *impressive*.

hmm, the K8 has an ISA from ~2002, so in the years since then, why 
would you expect no improvement from their competitor?  branch prediction
_is_ one of the relatively few places where architectural progress is 
being made, at least now that we're over the clock-is-everything era.

> It's very fair to compare woodcrest to k8, because the next generation chip 
> from AMD is K8L and as
> that must use 0.065 technology which will under normal circumstances take 

uh, Core2 is 64nm as well.  you don't really think Intel would try 
mass-producing 90nm chips with 4M cache, do you?

> till 2008 or so to get sold in shops,

that's too pessimistic - it looks to me like AMD's excecutions is pretty 
decent these days, and I expect to see some preliminary K8L results 
this year, and wide availability in 1H07.

> Basically first that K8L chip must tape out then it takes another year to 
> produce it and get it in the shops. That's how it normally works.
>
> But the combination of new process technology + moving from 3 to 4 
> instructions a cycle will of course give massive problems
> and headaches to AMD. Especially knowing the years of delay it took to 
> introduce previous technology (0.09) when it was new.

well, AMD's been vehement clear that your pessimism is untrue.

> In short AMD will have to release some quad core k8 end of this year to be 
> able to compete with woodcrest AND clock it to 3Ghz.

nah.  quad-core requires 65nm as well for decent yields, and it's not like
AMD's been sitting on their hands for the past 5 years.  I'm guessing they're
just waiting for the Core2 publicity to subside, then start showing off 
the K8L.

> Of course putting 2 more cores to k8 is simpler for AMD than to design a new 
> core that executes at 4 instructions a cycle.

that's a strange comparison - you must know that K8 is nominally 3x wide,
as the P6/P-M was, and that Core is basically "P6-L" (+1 decoder, etc)?
so AMD needs to go from 3 to 4.  tune up the branch prediction, bigger,
smarter caches, 128b/cycle sse, etc.

http://arstechnica.com/articles/paedia/cpu/core.ars/5

> That dual opteron dual core 2.4Ghz here is already nearly uncoolable.

don't be silly.

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