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Each hyperthreading CPU appears to the OS as 2 physical processors, this
has some up sides, and some down sides. It's similar to what some other
architectures have referred to as "Multiple instructions per clock cycle".
The up side is performance, while it's not as linear as SMP, it's a
performance gain just how much depends on your OS and applications. The
best numbers I have heard are 40% to 60% performance gain.
The down sides that I have seen are
- Some software licenses by CPU, and they want to charge for a 2
processor license when you have 1 hyperthreading processor.
- There is a data separation risk, it's possible for one process to
"see" another processes memory space, this is due to shared cache if I
recall correctly.
You can turn Hyperthreading off at the BIOS if you must.
Dual cores are 2 actual processors on one physical block. These are
truly seen as dual processors, the main difference between a Dual core
CPU and a system with 2 Xeons is the interconnect between the 2
processors, The dual core box has a really fast, dedicated connection,
where the standard Intel SMP box has the North Bridge and the South
Bridge to deal with for CPU to CPU, and CPU to RAM and IO devices.
A dual core box should perform as good as a dual Xeon system at worst.
At best it may do much better depending on what the type of work load is.
All of that said, I would expect this new Intel CPU to appear as 4 to
the OS and software. I haven't seen a real performance gain from
hyperthreading, but I haven't done very fine level studying of a system,
just the "feel of it". Dual core should offer real performance gains for
some things, but mostly it'll just behave as if it were an SMP system.
Kevin
Pat Regan wrote:
> Greg Brown wrote:
>>I'm not sure if the Intel Extreme is even for sale yet and in case you
>>haven't heard about it here is the skinny: it is a dual core
>>hyperthreading processor. A regular hyperthread processor will be
>>"seen" by the OS as a dual processor (this based on my scientific
>>study of how many penguins showed up on the screen at Knoppix boot) so
>>it would seem logical that this chip would appear as a quad processing
>>machine to the OS.
>>
>>So my question is will Linux behave with this processor in place?
>>Will it see and use all "four" processors?
>>
>
> I am sure it will act exactly like a dual processor Xeon server with
> Hyperthreading. It should show as two processors, but the scheduler
> does (should?) not treat it as 4 individual processors.
>
> Pat
>
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