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Re: Dual Core Or Dual CPU - What's the real difference in performance?



--- Cy Schubert <Cy_(_dot_)_Schubert_(_at_)_komquats_(_dot_)_com> wrote:
> In message
> <17866_(_dot_)_47828_(_dot_)_219523_(_dot_)_71972_(_at_)_bhuda_(_dot_)_mired_(_dot_)_org>, Mike
> Meyer writes:
> > Generally, more processors means things will go
> faster until you run
> > out of threads. However, if there's some shared
> resource that is the
> > bottleneck for your load, and the resource doesn't
> support
> > simultaneous access by all the cores, more cores
> can slow things
> > down.
> > 
> > Of course, it's not really that simple. Some
> shared resources can be
> > managed so as to make things improve under most
> loads, even if they
> > don't support simultaneous access.
> 
> Generally speaking the performance increase is not
> linear. At some point 
> there is no benefit to adding more processors. In a
> former life when I was 
> an MVS systems programmer the limit was seven
> processors in a System/370. 
> Today we can use 16, 32, even 64 processors with a
> standard operating 
> system and current hardware, unless one of the
> massively parallel 
> architectures is used.
> 
> To answer the original posters question, there are
> architectural 
> differences mentioned here, e.g. shared cache, I/O
> channel, etc., but the 
> reason the chip manufacturers make them is that
> they're more cost effective 
> than two CPUs.
> 
> The AMD X2 series of chips (I have one), they're not
> truely a dual 
> processor chip. They're analogous to the single
> processor System/370 with 
> an AP (attached processor) in concept. What this
> means is that both 
> processors can execute all instructions and are just
> as capable in every 
> way except external interrupts, e.g. I/O interrupts,
> are handled by the 
> processor 0 as only that processor is "wired" to be
> interrupted in case of 
> external interrupt. I can't comment about Intel's
> Dual Core CPUs as I don't 
> know their architecture but I'd suspect the same
> would be true. Chips in 
> which there are two dual core CPUs on the same die,
> I believe one of each 
> of the dual core CPUs can handle external
> interrupts.

 Wow I love ansking questions without too many
specifics as I learn so much more. With this however
it really seems to be a love hate relationship with
dual core.
 
 Based on what you stated above, would that mean that
when using a dual core system, using polling interupts
might be better or perhaps monumanally worse?

 
> I 
> have a mortgage so spending money on computers is
> not a high priority in 
> relation to that priority but dual core does give me
> an opportunity to 
> enter the market relatively inexpensively and get
> good value for the money 
> I spend on the technology. That's really what it's
> all about, how much 
> performance you get for the money you spend.
> 

 Tring to figure out the fud from reality is often the
best way to make sure you really get the best value.
However, it always seems to "depend" on many variables
:)


 Thanks!

  Nicole



> -- 
> Cheers,
> Cy Schubert <Cy_(_dot_)_Schubert_(_at_)_komquats_(_dot_)_com>
> FreeBSD UNIX:  <cy_(_at_)_FreeBSD_(_dot_)_org>   Web: 
> http://www.FreeBSD.org
> 
> 			e**(i*pi)+1=0
> 
> 
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