[petsc-users] KSP_SpeedUP

[Jed Brown]

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