[BANANA] Berkeley Lab - Scientific Computing Seminar - Friday, 08/22/2008, 1:00pm

[Esmond G Ng]

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