Application Performance Impact on Trimming of a Full Fat Tree InfiniBand Fabric.

We measured InfiniBand traffic in our full fat tree fabric and measured performance impact of trimming the fabric on our major application kernels. Based on traffic pattern analysis and application performance impact we infer that a 2:1 trimmed fat tree is a cost effective alternative to a full fat tree for this specific set of applications. The methodology we used may be useful for others who are performing design trade-offs for HPC systems. We also propose that switch hardware vendors design director class switches with trimmed fat tree options that optimize per port costs.