Date: Wed 29 May
Time: 15.00
Place: room 214

Speakers: Giovanni Chiola and Giuseppe Ciaccio
Title: An Active Message Layer for Linux Network of Workstations

Abstract. Networks Of Workstations (NOW) composed of fast personal computers configured with large quantities of RAM and hard disk, and running the Linux operating system are becoming more and more attractive as cheap and efficient platforms for distributed applications. The main drawback of this kind of distributed computing platform is the poor performance of the standard LAN interconnections based on RPC, sockets, TCP/IP, Ethernet, in terms of throughput as well as message latency. The use of Active Messages, where the raw hardware performance of network devices is brought directly to user application level, is one of the current research topics in terms of distributed systems architecture. The first commercial implementation of this concept was provided by Thinking Machines Co., for the CM-5 platform as a library called CMAML. The use of such library allowed user programs to define "handlers" to be associated with messages sent or received. These handlers are activated by the sender and receiver processors in response to interrupt signals generated by the network devices, by-passing several layers of kernel and network protocol software. In the literature such a by-pass is reported to be able to provide from 1 to 2 orders of magnitude improvement in communication latency and up to 1 order of magnitude in throughput as compared to the standard approach to communication implemented for high-speed local area networks of workstations using the same hardware devices. The Active Message principle has been followed in research projects developed in large research labs in the USA, such as the FM project developed at the University of Illinois at Urbana Champain on top of a NOW of SPARCstations connected by a fast network called Myrinet. In principle, the same idea can be applied to more standard, cheaper network devices such as 100 Mb/s Fast Ethernet based on UTP class 5 cables. The application of this principle requires changes in the structure of the Operating System kernel with respect to the one of stand-alone workstations with usual local area network interconnections, as well as the development of a library of communication primitives to simplify the task of programming distributed applications by defining handlers for messages. We are now designing and starting to experiment at DISI (see the GAMMA Project description) a modification of the Linux kernel that allows the use of 12 Pentium 133MHz machines equipped with 32 MB RAM and a 100 Mb/s Fast Ethernet card each as an efficient platform for running distributed applications of type Single Program Multiple Data (SPMD) or MIMD, with an active message layer for low latency, high throughput inter- processor communication. In the long run, a porting of the MPI standard environment on our active message prototype platform is envisioned. In this seminar we shall provide a general overview of GAMMA and some preliminary results that we were already able to measure on our prototype.