multi core os x machines

[Barry Smith]

   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
>>>
>>>
>>
>

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