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ACM Transactions on
Computer Systems, Vol. 20, No. 1, February 2002, Pages 49-83.
Fast and Flexible
Application-Level
Networking on Exokernel Systems
Gregory R. Ganger
Carnegie Mellon University
Dawson R. Engler
Stanford University
M. Frans Kaashoek, Héctor M. Briceño, and Russell Hunt
Massachusetts Institute of Technology
Thomas Pinkney
Vividon, Inc.
Abstract
Application-level networking
is a promising software organization for improving performance and functionality
for important network services. The Xok/ExOS exokernel system includes
application-level support for standard network services, while at the
same time allowing application writers to specialize networking services.
This paper describes how Xok/ExOS’s kernel mechanisms and library
operating system organization achieve this flexibility, and retrospectively
shares our experiences and lessons learned (both positive and negative).
It also describes how we used this flexibility to build and specialize
three network data services: the Cheetah HTTP server, the webswamp Web
benchmarking tool, and an application-level TCP forwarder. Overall measurements
show large performance improvements relative to similar services built
on conventional interfaces, in each case reaching the maximum possible
end-to-end performance for the experimental platform. For example, Cheetah
provides factor of 2-4 increases in throughput compared to highly tuned
socket-based implementations and factor of 3-8 increases compared to conventional
systems. Webswamp can offer loads that are two to eight times heavier.
The TCP forwarder provides 50-300% higher throughput while also providing
end-to-end TCP semantics that cannot be achieved with POSIX sockets. With
more detailed measurements and profiling, these overall performance improvements
are also broken down and attributed to the specific specializations described,
providing server writers with insights into where to focus their optimization
efforts.
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