Re: multi core os x machines

[Barry Smith <bsmith@xxxxxxxxxxx>]

  It depends on how the memory is connected to the individual cores or CPUS;

for example the AMD has a different approach than Intel. If the different processors/cores

have SEPERATE paths to memory then you will not see this terrible effect.

   Barry

On Nov 13, 2007, at 10:23 AM, Gideon Simpson wrote:

This is also true for a multi-processor machine, or its unique to multi-core machines?

-gideon

On Nov 13, 2007, at 11:14 AM, Barry Smith wrote:

  Not possible. The problem is that with one process it uses all the memory

bandwidth, when you change to use 2 processes (2 cores) each core

now gets only half the memory bandwidth and hence essentially half

the speed.

   Barry

   Barry

On Nov 13, 2007, at 10:06 AM, Gideon Simpson wrote:

Has anyone had any success in getting good performance on multi-core intel os x machines with petsc?  What's the right way to get MPICH up and running for such a thing?

-Gideon Simpson

 Department of Applied Physics and Applied Mathematics

 Columbia University