WSDLite: A Lightweight Alternative to Windows Sockets Direct Path
Evan W. Speight, Hazim Shafi, John K. Bennett · 2000
This paper describes WSDLite, a thin software layer that maps a useful subset of the WinSock2 APT onto a system area network. The development of WSDLite was motivated by our experience with an early version of Windows Sockets Direct Path (WSDP). WSDP is intended to allow unmodified applications to exploit the performance and reliability advantages of System Area Networks (SANs). This is accomplished through the use of a software "switch" that, when appropriate, redirects message traffic through the SAN provider protocol stack instead of the standard TCP/IP protocol stack. The need for WSDP to implement the entire WinSock2 APT results in substantial overhead. While we expect later versions of WSDP software to exhibit better performance, the beta version of WSDP examined was only able to achieve 26% of the native SAN Virtual Interface Architecture (VIA) throughput on our system. Although better performance can clearly be obtained by coding directly to the SAN native APT, this is not a particularly attractive alternative. It may not be desirable or possible to rewrite existing programs to use the SAN library instead of TCP/IP, since coding directly to the SAN provider interface requires exacting buffer-management by the programmer. Additionally, this practice results in applications that are network-interface specific, thus requiring software vendors to maintain multiple versions of their applications that are tailored for each network vendor's APT. Finally, it is likely to be infeasible, or at least unpalatable, to rewrite substantial portions of the large body of application code already in existence. A third alternative is suggested by the observation that many Windows network applications only utilize a small fraction of the WinSock2 APT. For those applications that do...