[cluster-l] Single- vs. Dual- vs. Quad-core CPUs

[Jim Phillips]

On Thu, 29 Mar 2007, Nils Oberg wrote:

> Will a memory-limited code benefit significantly by adding a higher-speed 
> interconnect?  Do vendors lend demo equipment to test these sorts of things?

By memory-limited I meant that your performance within a node is limited 
by memory bandwidth, memory latency, and/or cache size.  Just because you 
use a lot of data on a single node doesn't mean that you need to 
communicate a lot of data to other nodes.  It depends on the algorithm.

You can get a 10,000 SU development allocation at NCSA in under a month. 
It's a lot easier to test there than to borrow and install cards.

> Is there any way to determine how jobs are scheduled?  I'm thinking of the 
> case where a user runs an mpich job with 10 processors on a 5-node cluster 
> with 8 cores in each node.  Will mpich put 2 processes on each node, or will 
> it bunch them all on the first two nodes in its machines file?

The queueing system is generally responsible for that.  If you let Grid 
Engine schedule one slot per core then you have a choice of fill-up or 
round-robin based assignment in the config file.  You can also let Grid 
engine just hand out nodes and tell mpirun to use 8 processes per node.

-Jim