Berkeley Lab - Scientific Computing Seminar

Date:

Friday, August 22, 2008

Time:

1:00pm-2:00pm

Location:

Building 50A, 5132 Conference Room

Seminar Speaker:

Torsten Hoefler
Department of Computer Science
Indiana University

Title:

Networks are not Crossbars - A Case Study with Infiniband

Abstract:

Most large-scale applications employ collective or sparse communication patterns in order to achieve high scalability. A particular example of such patterns are the collective operations defined in the Message Passing Interface standard which map abstract definitions such as a global multicast/broadcast to network-specific implementations. While sparse communication patterns are often easy to map to current network architectures such as fat-trees, dense collective operations like all-to-all are likely to cause congestion and head-of-line blocking in most network designs. The performance of the most general endpoint-congestion free communication patterns can be modelled with a metric that we call effective bisection bandwidth. We analyze the influence of static routing on the effective bisection bandwidth and different communication patterns for fat trees. Furthermore, we discuss possible approaches to reduce head-of-line blocking with adaptive routing strategies. Another approach to mitigate communication costs results from more intelligent network interfaces. In this approach, we analyze the applicability of a new programming paradigm that encourages overlapping of computation and communication at the application level. We discuss tradeoffs for asynchronous message progression and different paths to solve this problem.

Sponsor of Seminar:

Paul H. Hargrove

Scientific Computing

Contact Esmond G. Ng EGNg@lbl.gov