[petsc-users] KSP_SpeedUP

[Barry Smith]

   Second bullet at http://www.mcs.anl.gov/petsc/petsc-as/documentation/faq.html#computers

    Barry

On Apr 14, 2010, at 4:10 PM, Jed Brown wrote:

> On Wed, 14 Apr 2010 18:02:11 -0300, Pedro Torres <torres.pedrozpk at gmail.com 
> > wrote:
>> Hello,
>>
>> Sorry if this questions its not appropiate for the petsc-list, but  
>> I really
>> want to known what happen when I'm getting differente KSP time  
>> results. For
>> example, allocating two process in the same node I get 6.24 sec,  
>> and when
>> allocating two process in two nodes (1 process per node) I get  
>> 4.7sec.   Is
>> there a memory contention problem in my node?? The problem get  
>> worst when
>> increase the number of process.
>
> Sparse matrix kernels are primarily limited by memory bandwidth which
> does not increase much with multicore hardware (vendors rarely mention
> this).  When you use multiple cores per socket, they have to share the
> available bandwidth, so you get lower performance.  It's *usually*  
> still
> faster to use the available cores, but the per-core performance is
> definitely lower than when using only one core per socket.
>
> Jed