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From: Tim Johnston <>
Date: Mon, 07 Jun 2004 10:45:00 -0400
Message-ID: <>

Excellent... Thanks Matt... I have a couple more questions below if you have the chance... Thanks...

Matthew Zito wrote:

> The dodgy parts about it is that while it is two separate instruction
> cores, there is shared cache, which is a bit of a performance hit, and
> the cores share access to the memory bus, which can also be a
> performance hit.

I read some of the stuff about the common memory bus and figured that would be an impact... As far as cache, it appears that each core has it's own L2 cache... Kind of... They appear to share the bus to the L2 but the L2 is doubled from 8 to 16 MB and each core has a dedicated 8 MB... They perform some magic to split the address ranges on the L2 bus and it makes sure that each core can only access the appropriate section of the L2... Any thoughts on that?

> But - since you're not actually increasing clock speed, you're
> increasing parallelization, are you actually doubling your
> performance? Depends how you define that. Any single thread is going
> to execute at pretty much the same speed (there is a bit of a clock
> speed jump from the IIIs to the IVs, to be fair), but you'll be able
> to run twice as many threads at once, so there's less time waiting in
> the scheduler queue. But, this is not the same thing as a doubling of
> execution time, so its a little disingenuous to claim a doubling of
> performance.

Ok... To give this a real world example, if you have a 12 CPU box that has an average of 12 processes running CPU bound then moving from III to IV doesn't buy you much... But, if you have a 12 CPU machine with an average of 24 CPU bound processes then it should help...

> The REALLY important thing, though - Oracle counts every core of a
> multi-core processor as a processor. This means if you swap 8
> Ultrasparc IIIs for 8 Ultrasparc IVs, you have to license a total of
> 16 processors for Oracle. The US IV is not the normal situation of
> "get a processor upgrade to improve performance without licensing more
> processors " - this physical upgrade requires that you buy more Oracle
> licenses. Needless to say, sun is not particularly thrilled about
> that, but since Intel and IBM have also said that multi-core CPUs are
> the way of the future, Oracle has taken a stand early on that every
> core counts as a processor and must be licensed as such.

Ah... I hadn't heard this one yet... That could be a big one... Thanks!

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Received on Mon Jun 07 2004 - 09:41:23 CDT

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