Re: Beoboard idea

[Simon Thorpe <thorpe@xxxxxxxxxxxxxxxxx>]

>	Douglas Eadline <deadline@xxxxxxxxxx> wrote:
>
>	And what is the limit of CPUs you can put in the machine. This
>	will limit problem size (scalability).
>
>The number of CPU's you can put into the machine is limited by the 4GB
>PCI memory space. For performance reasons I map all memory of all SA's
>into the PCI memory space, this limits the number of CPU's to 64 if you
>use 64MB of RAM per CPU. Obviously the host system needs some of the
>space as well so i guess the limit will be 56 CPU's. Multiple hosts with
>56 SA's can be networked together of course.
>
>greetings,
>
>Mark.

A couple of comments.

One is that Simtec will also offer CPU modules with 32 Megs. In this case,
you presumably would be able to get 128 modules in the 4 Gigbyte memory
space - let's subtract 512 megs for the host, which leaves120 modules.

The other is that I believe that by configuring the 21285 PCI Bridge you
can declare parts of the memory as local, and other parts as public. If so,
it might be possible to have, say, 32 Megs of local memory and 32 Megs
available for shared memory per processor. Again, you'd be able to get back
up to 120 CPUs...

Course, all this is hypothetical - I haven't got the cash. And the question
of whether it's worth it depends on how well the thing works.But it's nice
to think about it anyway..

Actually, if the Sebring ring idea works, you could imagine a board with 2
sebring ring chips, each driving 4 CPU modules, and that these boards could
be linked up in a ring with Gigabytes/second of communications bandwidth.
In that case you could really take advantage of those 4 Gigabytes of PCI
memory addressing....  :-)

Cheers

Simon



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Simon Thorpe
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