Latency and bandwidth considerations in parallel robotics image processing
J. A. C. WEBB · 1993
Parallel image processingfor robotics applications differs in a fundamental way from parallel scientific computing applications:the problem size is fixed, and latency requirements are tight.This brings Amdhal 's law in eflect with full force, so that message-passing latency and bandwidth severely restrict performance.In this paper we examine an application from this domain, stereo image processing, which has been imple- mented in Adapt, a niche language for parallel image processing implemented on the Carnegie iWellon-Intel Corporation i Warp.High performance has been achieved for this application.We show how a I/O building block approach on i Warp achieved this, and then examine the implications of this performance for more traditional machines that do not have i Warp's rich I/O primitive set.For example, it does the robot no good to begin processing a new image before the last image is acted upon; doing so can cause the robot to doubly compensate for an inaccuracy in steering, and lead to instability in the control algorithm.WJe would like to speed up this cycle through the use of parallel computers.This paper addresses the perceptual issues, namely capturing and processing sensory data.This tends to be a major bottleneck in such systems, since images are large and often sig-C31993 ACM 0-81864340-4/93/0011 $1.50 Capture Sensory Data Process Sensory Data Parallel systems are widely recognized to be increasing in message passing bandwidth, but latency is not decreasing as rapidly.As we apply more and more processors to a particular problem, message passing latency plays a greater role in limiting overall speed