Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
Rob Stow wrote:
> Ben Pope wrote:
>
>> I guess it depends slightly on what you are doing.
>
> You seem to have found the TechReport benchmarks.
After my guessing, yes, I did.
> From those it seems clear that it does *not* depend on what you are
> doing. An Opty 275 beats a single or pair of Opty 248's in *everything*
> even though both the 275 and the 248 are 2.2 GHz chips.
Except raw memory bandwidth tests (not that it actually 'counts' in real
life).
> > With 2 seperate
>
>> Opterons, you have 2 memory busses, with a dual core, you have one.
>
>
> True enough. However the memory controller in the dual-core Opterons is
> supposed to be better and faster.
Yes, something I hadn't accounted for.
> As well, whether you have two single-core chips or one dual-core chip,
> in order to maintain cache coherency each core has to snoop the caches
> on the other core before accessing main memory - which adds substantial
> latencies to the RAM accesses. In a dual-core Opteron those additional
> latencies should be substantially reduced because there is no need for
> one core to go off the die to take a peek at what is in the other core's
> caches.
Or indeed, even over the Hypertransport link. SRI sorts that one out at
full whack. Something else I didn't know about. AMD have really
thought about their design.
> Hence, a pair of single-core Opterons should have a substantial memory
> bandwidth advantage over one dual-core Opteron. However, the daul-core
> Opteron will have a big latency advantage. And, as we have seen in AMD64
> vs (P4 and Xeon), reductions in latencies almost always do more for your
> performance than bandwidth increases.
Indeed.
> A search at AnandTech will get you latency numbers for the single-core
> Opterons but it will probably be a while longer before they have similar
> numbers for the dual-core chips.
>
> I expect a better explanation than my stumblings to also show up soon at
> places like AnandTech and Ace's Hardware. I'm still struggling to
> digest all I have read over the past few days.
The Techreport article is actually very well written and informative, I
felt. Will have to start going there more often.
Looks like the Athlon FX2 will probably arrive at around the £500 mark,
which will probably put me off for a while. Enough speculation, anyway.
I grabbed my Winchester a month ago and now there are Venice cores
available... the duals have the same advantages as the Venice, namely
SSE3. I like.
Ben
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